739

CHAPTER XXX.

SHROPSHIRE.

By Professor CHARLES LAPWORTH, LL.D. F.R.S. F.G.S., and Professor W. W. WATTS, So.D., F.R.S., F.G.S.

INTRODUCTION.

H R OP SH I R E is not equalled by any other English county S of similar size in the variety and interest of its geology. It was the scene of some of Murchison's most important work and the type locality of his Silurian System. Its rocks have been investigated by Prestwich, Aveline, Mr. Maw, Allport, Prof. Bonney, Dr. Callaway, and J. F. Blake, to mention only a few of the chief workers. With very few exceptions it shows all the chief Rock Formations from the Archsean to the Lias; fossils are numerous, and in the older fossiliferous rocks well preserved owing to the absence of cleavage; there are igneous rocks belonging to at least four periods; the several coalfields belong to different types; there is a rich and almost unworked field of glacial deposits; and numerous structural and physiographic problems still await solution.

PHYSICAL ASPECT.

Physically, as well as historically and ethnographically, it represents the contact zone between and . Its western and southern hills are the continuation of those of Wales, abutting upon, and plunging under, the Triassic Plain of Cheshire and the Midlands. As wave after wave of eastern invaders has broken upon the hill margins, held by their native tribes, so has Formation after Formation been pushed westward from an eastern sea, each over­ lapping its predecessors, finding foothold on the rocks of the same hill margins and coming to rest on the relics of ancient landscapes. This feature was first noticed by D. C. Davies and afterwards emphasised by J. F. Blake, who rightly attri­ buted it to the stubborn resistance of the rocks to denudation and to the recurrence of earth-movements along old but sensitive coast lines. The main unconformities are the following: (1) At the base of the Cambrian; (2) beneath the Bala Rocks; (3) below the Upper Llandovery; (4) at the base of the Carboniferous; (5) at 740 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME.

the base of the Trias; and (6) under the Glacial deposits. It is more than possible that there may be others; one, according to Blake, under the Torridonian, another under the" Permian," and possibly others within the mass of the Trias. As a consequence of the unconformities certain members of the sequence are missing, the chief being part of the Cambrian, the highest part of the Ordovician, the lower part of the Silurian, and at least the upper part of the Permian; while the Lower Carboniferous rocks are very poorly represented except in the north-west. All Formations from the Middle Lias to the Glacial are unrepresented. Physically the county is divided into two very distinct parts­ an Upland region to the south and west, founded on Palseozoic rocks; and a Lowland, of Triassic and newer rocks, to the north and east. The boundary between the two is naturally irregular. It is to some extent defined by the course of the Severn, but this river both emerges from, and plunges back into, Palaeozoic ground, never, however, departing very far from its edge. When viewed from such an outpost as the Wrekin the Northern Plain appears flatter than it is in reality, but even from such a point there are outstanding Triassic scarps like Nesscliff, , and Hawkestone, and parts of the county are covered with glacial mounds and meres. The Upland varies much in character from point to point. There is the deeply incised Plateau of the Longmynd, a type of landscape not easily matched elsewhere; the steep-flanked, sharp­ edged, Hogsbacks of the U riconian Hilts; the mountainous Ridges of the highly-inclined Ordovician rocks of Shelve, the Stiper Stones, and the Breiddens, with their massive igneous cores and cones; the Edges, rocky or timbered, of the Silurian and eastern Ordovician, ranging north-east and south-west; the smooth and partly cultivated Moorlands of the limeless Silurian; the less clearly featured Coalfields; and the garden and orchard land of the Old Red Sandstone, culminating in the dolerite-capped Buttes of the Clees. Industries and occupations are linked with altitude, climate, and rocks. The great plain is richly cultivated, with but few in­ dustries save those connected with agriculture. Even here there is stone and water to be got from the Trias, both of ex­ cellent quality. There are coal, iron, and clay industries in the coalfields; lead has been worked in the Ordovician hills from the time of the Romans, and zinc and barytes in later times; road­ metal and building-stone are obtained from the igneous rocks, quartzites, and sandstones, mainly in the Ordovician areas; the Silurian limes have been long important for smelting and build­ ing. Sheep, cattle, and horse breeding are carried on over the whole county, and besides the usual crops and grass there is a great deal of fruit grown in the south. The Geologists' Association has made five visits to different FIG. 122 •

.... '

~ T, ffi Po< ~ ::::1en

SHROPSHIRE Sc~/1or Mile s t 1 { r__~

T his illap is based on the Index Map of Wa les, Sheet 15. of the Geo logical Survey, with mod ifications ta ken from the papers of Dr. C. Callaway and Professor J. F. Bla ke, and from unpublished observations by Professor C. La pwort h a nd Professor \ V. \V. \ \'atts. T be scale docs not admit of the introduction of more min ute sub-divisions, although these have been mapped , nor doc s it all o w or morcf lm n a diagrammatic rcpre senrati on in many parts. 742 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME. parts of the county and its neighbourhood. Indeed, one of the earliest "long excursions" was that to the district in 1872, under the guidance of Professor John Morris and Messrs. La Touche and Lightbody. The southern part of the county was visited again in 1894, the Ludlow district in 1904, and was the centre for the Berwyn excursion in 1876, and again in 1908, under the late Mr. J. Lomas. The notices of these excursions, and especially the paper written for that in 1894, have been freely laid under contribution in the following account, but little is said of the north-western district, on which some notes will be found in Lomas's description of the Berwyns,* In such an account as this it is difficult to avoid a slight trespass over the borders into Montgomeryshire, and other neighbouring counties, where the political boundaries pay little respect to those of the rocks. The Breiddens, the Long Mountain, and parts of the Shelve and Ludlow areas are treated as though entirely in­ cluded in Shropshire. Among the works dealing with the geology of the county may be mentioned Murchison's" Silurian System," Symonds' "Records of the Rocks," La Touche's" ," " " (Geology by E. S. Cobbold), and Randall's" Severn Valley."

PHYSICAL STRUCTURE.

For the purposes of description the central feature of the county may be taken to be the Longmynd Plateau, around which the Formations are grouped in rough symmetry from the Long­ myndian to the Old Red Sandstone. This rude dome is covered and invaded, mainly from the north and east, by Formations ranging from the Carboniferous to the Lias, the main part of them constituting the northern plain j but tongues and outliers often press to the south and west, giving rise to a very irregular boundary line (see map, Fig. 122). The Longmynd, however, although one of the oldest rock-groups in the county, is not a simple anticline. It is broken off by faults on its eastern and western margins, while its northern and southern borders are overlapped by newer Palseozoic or Mesozoic rocks. The order and relations of the oldest rocks are by no means assured, and more work requires to be done, or at least published, before it is possible to speak with certainty on this subject. One thing is certain, that there is here a great thickness and variety of volcanic and sedimentary rocks of pre­ Cambrian age. A general idea of the relations of the older rock systems may be gained from the study of the section (Figs. 123 and 124), drawn across the southern part of the county.

"Proc, Geol, Assoc., vol. xx (1g08), p. 477. SHROPSHIRE. 743 BASEMENT OR PRE-CAMBRIAN ROCKS.

Owing to the faulted relationship of the oldest rocks, and to the fact that inversion is not infrequent, the apparent stratigraphy of these rocks cannot be trusted to furnish absolute evidence of relative age. In the absence of fossils we are driven to depend upon lithological character and the evidence of contained fragments, both classes of testimony accompanied by special difficulties in this case. Lithologically there are four distinct groups of rocks; the Rushton Schists, the Granite and Gneissose rocks of the Wrekin, the Uriconian Volcanic Groups, and the Sediments, largely composed of volcanic material, of the Longmynd. The separation of these types must not be taken to indicate their entire independence of one another, nor must it be assumed that the order of description indicates their relative ages.

THE RUSHTON SCHISTS. Near the village of Rushton, two miles west of the summit of the Wrekin, Dr. Callaway* discovered a small area of quartz­ mica-schists. No pebbles of this rock have so far been found in either the Longmynd conglomerates or the Uriconian conglomer­ ates of Charlton Hill. The schists may possibly represent a highly crushed form of gneiss like that of Primrose Hill, but Dr. Callaway considered them an independent group.

GRANITIC AND GNEISSOSE ROCKS. A large "gravel" quarry in the Ercal, the northernmost member of the Wrekin chain, shows exposures of aplite in con­ tact with tuff. The mutual relationships are masked by faulting, but such evidence as there is is in favour of the intrusion of this rock into Uriconian tuffs. Granitic and dioritic rocks, often foliated, are also exposed on Primrose Hill, at the southernmost end of the same chain. These have been regarded by some] as an ancient foliated series, like the Malvern gneiss, but by others t as merely a modified form of the Ercal aplite. The poorly ex­ posed sections have been interpreted according to both views, one of which would make the rocks earlier, and the other later, than the mass of Uriconian tuffs and lavas.

URICONIAN ROCKS. The term Uriconian has been applied to certain disconnected groups of ashes and lavas, mainly rhyolitic in composition, which

* Geol. Mag., dec. 3, vol. i (1884), p. 362. t Quart. [ourn; Geoi, Soc., vol. xxxv (1879), p. 652. ~ Quart. [ourn; Geol, Soc., vol. xlvi (IBgo), p. 408. e:: ~ "0: a Dab , ~ c :! '/~ ::: 0 /~ ~( o el )' Golfa , Z n'" :; r- :< ~liddl et own . e- ~. !" "=: ?i ;; ...... ," I• :::l t"" ':' c, 0 :< I Llandovery. Vl I. " 4- '"0' Q'" 0' W enlock c :< <3 z 3 Ludlow "> 0 ~ > =.~ ('l <:.. '" ~ 3 ~ ~ C: W enlock, til ~( art on . til s So :;" ..... :< -< '"~O:: ~ ; '"...;til ., '" Llan dover y, ~ ""'l'" " Z ;'§' 0 - :-.~ I ~ [ .:: .c:; ..§.;: C'l -: '" '" Chlrbury. ,... ., til ~-~. :.. s:. = ~ :T Bala . "~ e '" "" ~ 'g- ~... ,~:: '" -e ~ :::l 0 I,)~ Hagle)'. r: :-=:0 4- ", _ ::: ... ;:::' L1andeilo E: ~-i '"~'"- a 51')' Burn. ~ 0 " ? ~:t1 '" ~ 0" ~liddl e l on . 0 :;: n ; :::~ =::; n'" --' =-~ :; St ap eley H ill. 0 ~ :< :<" '"::l '", .. 1; ::!..w Aren ig :< ~ 0'-' Shelv e. 7- _ 0 v n 5' ii' '" '" .. as. Venus Bank , "e; o'n :-< ill :::l~ ...; . '";;' 5nail beach 0 ...; "5. St iper St ones. '" '"s; - '" Habberley 8 S, ...... Val ley• C'i ., Volc an ic '" ~ . or i Uriconlan . Pont esford Hill ;; ? 4- I ...... ::i Western x Longmy nd or (n Red Sane! \\\~\,~\ , ~\, i'l P ulvcrba tc h, stone Series, ':i:VIfi'IOA :i:i"Imnf NOI.LVIJOSSV , S.LSIDO'IO:iD ttl LO:-

Lo xrm vxn. C AN.AUOC D IS TIU CT. C O N.\"i":UA LI·:. B ROW S C L E F..

~ Ul -;;; .c c ;,.: t: o ,;, C .; g ,;, .. .; ...c c ""~ ~~ ;;. "c ~" c > ti~~ ~ .s.t: N .W. ~ ] (; ..::" " s 0 1 " c, U cn :::l UUU"" :;j U" -e ~ rr, :r: ...... ~ a~ , <,-....::....~.., "l ~ ~I,~ r ...... Ul S Ii ..;..; ., . .,. ~ ~ :: C g o "0 o " .s .!:: t- .§ M ":;:l r:; ~ :: ~ :: ] e ~ ~ .;, .!! ... ~ " -c "" "":J U ~ ~~ .~ 50 " 0 ~ s ·U]~! = 8 ":;l ;; j ~ ~ ~~;'JJ "0 '': ::: U :: E 's :,... ;:.J ::: CJ~ ~ ~ ~u t.ll V) j en :s.: c ~ " !;1 ~ : :l :: q ""E -:::: ..'3" . e..<::>:

LOSG~I\·XJ)IAS. C..\~rnRIAS: : O Rl>OVI CIAX, S It.L'R IA S'.

l a l • Easlern l.ong mynd or Gr ey e . Sh incton S ha les. I. Ba la , Ca radoc, or Chirbur y i. \\"enlock Limestone Sh aIe Se ries. d . S uper Gr oup ~ Aren ig Series. j. Lower L udlow Rock, . 1 Il~.Western Longmynd or Red d~t :\IYllon Flags Sh~h'e 1: • Upper Llandovery Sand- I:. ,\ Ylllest ry Lim estone. Sa ndstone Ser ies. . I II ope S hales. Series. stone, Congl omerate, a nd I. lJ pper Lud low Rocks. n. Uri conian Volca nic Series. d l . Stapeley Ashes. Limestone, O . R.S .·=Old Red Sand stone.

dtllelon I:~. ~L= Coal e'. <).uarLzile. e. Llan deilo or ~Ii P ur ple Shal e. C. Xlea surcs. e~.Comley Sandstone, Se ries. h. Wenlock Shale. D. = Dolerile. -., .j.., en 746 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME. occur along two main lines stretching north-east and south-west, one on the eastern and the other on the western side of the Long­ mynd. The eastern* line, that of the typical Uriconian, begins at Lilleshall Hill, reappears at the Wrekin, south of which it is joined by a line running from Wrockwardine and Charlton, passes south to include the Caradoc and Cardington Hills, and is finally seen at Warthill Knoll, near . This is a line of profound disturbance, bounded westward by the great Stretton-Charlton fault, beyond which the Longmyndian is largely covered with skins of Deuterozoic or even Protozoic rocks. East of the fault the sequence is fuller, and the natural junctions are often found showing the normal succession from the Cam­ brian upwards j still, even here much disturbance occurs. The westemt line of volcanic rocks, which runs south-west from Pontesford Hill, is also a zone of disturbance, limited by a fault on its western side, but here the strata beyond the fault belong to the Upper Cambrian (Shineton Shales).

FIG. 12j.- SECTlO:-; AC iW S5 CHARI.TO:-: IIILL.- C. Callaway. (Repr i/lt,, 1 by permission of tilt Council of th» Geolog ical Society .) [Quart. J OU/1l . Geol , S oc.• \ ·0 1. xlvil , p. 116.1

c Conglomerate. I Ande siti c lava, I: Grit. Iz Willeflinta. P Peb bly Gr it. q Cambrian qua rtzite. PI: Grit and pebbly grit. The volcanic rocks vary very considerably, both in sequence at a single spot, and in the different hills where they are exposed. The dominant rocks are pink or green rhyolites, usually with marked fluxion structure and are often perlitic and spherulitic. There are devitrified glasses still exhibiting the structures charac­ teristic of these rocks. This may be well studied at Overley Hill (Lea Rock), near Wellington, on the south side of the Ercal, and at Pontesford Hill, t where, among other structures, large litho­ physes occur. Acid tuffs, breccias, and agglomerates are of frequent occur­ rence, and may be observed at the great quarry of Lawrence Hill, or at Pontesford Hill. Grits and finer ashes often make thick beds, and outbursts of impalpable volcanic dust are now consolidated into hard, banded, halleflintas, like those so charac­ teristic of Lilleshall Hill.§ Less acid lavas and tuffs, andesitic • Quart. J ourn. Geol. Soc., vol. xxxv (1879), p. 643. t Quart. [otcrn, Geol. Soc., vol. xxxviii (1882), p. 119. :t: Quart. Journ. Geot, Soc., vol. Ix (1904), p. 450. § Quart. Journ. Geol. Soc., vol. xxxv (1879), p. 645. SHROPSHIRE. 747 in composition, occur interstratified with the more acid, and Pro­ fessor Boulton has described from Pontesford Hill* numerous beautiful and well preserved palagonite tuffs. The Charlton Hill section shows a conglomerate containing pebbles not only of the rhyolite but of a rock indistinguishable from the Ercal aplite. The strike of the volcanic rocks is east and west in the Wrekin, but it is elsewhere usually north-east and south­ west. The succession is much confused by intrusions in the form of dykes, sills, and laccolitic masses of basic rock. t The pre-Cambrian age of the Uriconian Rocks of the Wrekin, Charlton, and Caradoc, and their unconformable relation to the Cambrian, are made quite certain by the presence of fragments derived from them in the base of the Cambrian Quartzite j while the lithological character of the rocks is allied to that of pre­ Cambrian volcanic rocks elsewhere in Wales and the Midlands, as at Llanberis, St. David's, the Lickey Hills, and Nuneaton. Further observations on the age of the rocks are made in the next section. LONGMYND ROCKS. The rocks of the Longmynd, formerly classed as Cambrian and correlated with the Harlech and Llanberis groups, are found to be also of earlier date than the fossiliferous, truly Cambrian rocks of the county, which were overlooked until 1878. In the northern parts of the Longmynd the strata usually dip easterly, but in the centre and south the beds dip westerly throughout, indicating a thickness of not less than four miles of rock. The base of the visible succession is found in the shales of Church Stretton. There is a general agreement that the rocks are capable of division into two groups. The older of these, gener­ ally known as the Eastern or true Longmyndian Group, is dominantly grey in colour and consists of shales and slates, grey, green, or purple, interbedded with hard greywackes. The younger, dominantly red, is known as the Western Longrnyn­ dian, and is probably closely related to the Torridonian rocks of Scotland. The most striking rocks are massive, but not very constant, beds of conglomerate, with grit beds and some subordi­ nate slate. Details of the lithology of the two divisions will be found in J. F. Blake's paper.j Blake was of opinion that the red series rests unconformably on the grey. He classed the grey series with the upper part of his Monian System and the red with his "Lower Cambrian Series." In his red series he also placed certain red sandstones found at and other localities east of the Longmynd. He did not admit the correlation of the western volcanic masses *Quart. JOU1'n. Geol. Soc., vol. Ix (1904), p. 450. t See also E. S. Cobbold, "Church Srretton-e Geology,' p. 97. t Quart. [ourn. Geol. Soc., vol. xlvi (,890), p. 386. 748 GEOLOGISTS' ASSOCIATION JUBILEE VOLUMI:.

(Pontesford Hill, Chittol, etc.) with the eastern group (Wrekin, Caradoc, etc.), but regarded them mainly as intrusive. On discussing the eastern volcanic group, he was doubtful whether it should be referred to his "lower Cambrian" or to a separate pre-Cambrian group. In either case it would appear that he regarded the group as younger than the grey series, but older than the red series. Dr. Callaway,* on the other hand, finds pebbles of rock indistinguishable from Uriconian not only in the red but in the grey series. He, therefore, considers the order to be, (I) Uriconian, (2) Grey Longmyndian, (3) Red Longmyndian, and he is unable to find any evidence for the alleged unconformity between (2) and (). t Fossils are almost limited to the occurrence of worm­ tracks in certain beds, particularly in the lower division j but Salter found in the same division dubious impressions re­ ferred by him to Palaopyge and Dikellocepltalus, which are preserved in the Museum of Practical Geology j Blake records the occurrence of Lingula-like forms from the grey series. As we have already indicated, much yet remains to be done among the Shropshire rocks referred to the pre-Cambrian. It may, however, be of service if we give here (1909) the apparent descending sequence of the various lithological groups as they occur where these rocks attain their widest east to west extension, the nomenclature being that employed by one of the writers (Prof. Lapworth) in mapping the country. Linley (or Pontesford) Volcanic Series (TVestern Uriconian of Callaway). Green shales, purple and green grits, andesitic and rhyolitic lavas and tuffs. Series (Western Longmyndian). Group j-red and purple grits and shales, with conglomerates. Bayston Group j-red and grey grits, with the three zonal conglomerates of Stanbach, Darnford, and Haugh­ mond j the last rich in pebbles of volcanic rocks. Stratton Series (Eastern Eongmyndian). Portway Group j-purple, grey and green shales and flags, with the Narnells grit and conglomerate band near the base. Lightspout Group j--massive grey and green grits and flags, with few shales. Synalds Group j-purple shells and occasional flaggy grits and green shales, with the Carding Mill Grit at the base. Burway Group j-grey-green flagstones and shales, .having as a basement band the siliceous Buckstone Grit.

• Oseart, [aurn, Geot. Soc., vol. xl i i (,886), p. 4~" t Sse also E. S. Cobbold, op. cit., p, 72. SHROPSHIRE. 749 Stretton Shale Group j-eonsisting of b. Brockhurst Shales j-hard grey-blue and dark green laminated shales, with rare calcareous nodules. a. Watling Shales j-green shales, with occasional purple mudstones, flaggy beds, and rare cal­ careous bands. Cardington Volcanic Series (Eastern Uriconian of Callaway) of the Cardington and Caradoc Hills, etc. j- Andesitic and Rhvolitic lavas and intrusions j tuffs, volcanic grits and shales, pierced and locally overlain by dole­ rites and melaphyres. Along a line drawn east and west through the town of Church Stretton the Groups named above. follow each other geographic­ ally in the order given. Generally speaking, the rocks dip west­ ward, but the section is interrupted immediately east of that town itself by the two faults of the Stretton Valley, which there let down the wedge of Silurian rock between the Brockhurst and the Watling shales. The thickest of the Longmyndian Groups is that of Ratling­ hope, the outcrop of which occupies almost half of the Long­ myndian area. That having the longest visible extent is the Bayston Group, whose various disconnected outcrops occur along a north-north-east and south-south-west line ranging from Haughmond Hill to Asterton, a distance of between seventeen and eighteen miles.

THE CAMBRIAN SYSTEM. The Cambrian System of Shropshire consists of three litho­ logical members: 1. Wrekin Quartzite. 2. Comley Sandstone. 3. Shineton Shales.

LOWER AND MIDDLE CAMBRIAN SERIES. Quartzite.-The Uriconian hills of Caradoc and Cardington are flanked on their eastern sides, and the Wrekin on its western side as well, by a quartzite which rests unconformably against them, and contains in its basal beds fragments of rhyolite and tuff derived from them. This rock may be correlated with the Assynt Quartzites and with those of Nuneaton and the Lickey. T he Comley Sandstone is found east of the Wrekin and Caradoc chain, and at Lilleshall, and is a softer rock, containing basic derivative material and grains of glauconite. This was first named by Dr. Callaway the Hollybush Sandstone* and correlated with the rock of that name in the Malvern range. The Comley Sandstone is separable into a lower and an upper divi­ sion, and the basement beds of the latter can be seen overlying the rocks of the former in the well-known Comley Quarry, where • Quart. [ourn, Ceol. Soc., vol. xxxiii (,877), p. 662. 750 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME. the limestones of the lower division, characterised by the presence of Olenellus callavei, are succeeded by calcareous conglomeratic grits with Paradoxides groonzii. Other fossils, such as Kutorgina, Linnarssonia, Hyolitltellus, and Protospongia, have been collected from either the limestones or the sandstones. Ex­ cavations recently carried out by Mr. E. S. Cobbold on behalf of a British Association Committee have fixed the line of separa­ tion between the two divisions and shown that both are fairly rich in fossils. In December, 1909, Mr. Cobbold described to the Geological Society a considerable series of trilobites, includ-

FIG. 126.-SECTION ACROSS THE WREKIN, NORTH.EAST END.­ After C. Callaway. (Reprinted by permission of the Council of th, Geological Society.) S.E. N.W.

,2 . I Faults. Fault. (Scale-about 8 inches=I mile.)

1. Bedded Pre-Cambrian volcanic tuff, dipping north. 2. Quartzite. 3. Comley [Hollybush] Sandstone. 4. Shineton Shales (Upper Lingula Flags and Tremadoc). ing Protolenus, Microdiscus, Ptycho-paria, and Micmacca (?), found by him in the Olenellus Limestone and in the grey lime­ stones above it. * The local Series comprises the higher part of the Lower and the lower part of the Middle Cambrian. The first known fossil of the Comley Sandstone was quoted by Dr. Callaway from Neves Castle in the Wrekin District in his original description of the Formation. From the same locality Mr. Rhodes collected later (1891-2) examples of Paradoxides resembling P. tessini or davidis and P. rugulosus.

UPPER CAMBRIAN SERIES. The Shineton Shales constitute the highest division of the Shropshire Camhrian System. They are about 1,500 feet thick, '* Quart. [ourn, Geol, Soc., vol. lx vi (1910), p. 19. SHROPSHIRE. 751 and occur on the eastern side of the outcrop of the Comley Sand­ stone at the Wrekin and near Cardington. T hey also occur on the west of the Longmynd, running pa rallel to the western margin of that range and dipping under the Ord ovician Rocks. They are generally dark blue micaceous shales, weathering olive and yellow j they are uncleaved and have yielded fossils at two main horizons. Dictyon ema sociale occurs well down in the sha les in Mar y Dingle and in Cardi ngton Brook, where H ymenocaris is also met with. Much higher up, in Shineton (Belswardine) Brook,* there is a rich tril obite fa una comprising Asaphellu s Itomfra yi, Olenus triarthrus, Euloma, Niobe, and S humardia. t T he Shineton Shales may be correlated in pa rt with the upper Stock­ ingford Shales of Nuneaton and with the Grey Shales of Mal­ vern. t They doubtless represent the Tremadoc, and possibly pa rt of the Upper Lingul a Flags, and, if so, representatives of the Lower and Middle Lin gul a Flags, appear not to have been hitherto detected in the county. This may be explicable by a f ault between the Shales an d the Comley Sandstone east of the Wrekin, or by an unconformity.

THE ORDOVICIAN SYSTEM.

There are three areas of Ordovician Rocks in Shropshire, each with peculiarities of its own. The Caradoc area is wholl y in Shropshire , but the Shelve and Breidden areas, separated by the Long Mountain syncline, tr ansgress into Montgomeryshire. T he fullest sequence is seen about Shelve, but only the Bala division is at pr esent known in the other two areas. In the Ca radoc area an unconformi ty exists at the base of the Bal a Rocks j and in the Breidd en H ills, the Severn alluvium and probably an important fault mask the lowest beds of that Series. T HE SHELVE AREA , between the Longmynd and the Long Mount ain , which centres on Corndon Hill and the mining ground of Shelv e, may be taken as a type, as its sequ ence is th e most complete, the Arenig , Ll andeilo and Bala divisions being all well represented. There is no evidence of unconformity, and the lowest beds of the Stiper Stones Quartzite appear to rest con­ formably on the Shineton Shales previously described. § The succession is given below, and the rocks cover a large area of country on account of their repetition by a synclin e at Ritton Castle and Cefn Gwynlle and by the anticline of Shelve Hill and Com don (see Fig. 130, p. 767).

* Qua rt. Io urn. Ceoi. S oc., vol . xxx iii ( 1877), p . 65:2 . t See Ge ol ; M ag ., dec. 2, vol. v (18 78), p . 188. t Quart . f onrn, Geot . Soe ., vol. Iv (1899), p . 159. § P roc, Geol. A ssoc., vel, xiii (18 9)), p, 297. i 52 GE OL OGISTS ' · AS S OCIATION JUBILEE VOLUME.

Sh elve. Breidden. Car adoc.

:-- I 0:: ! ::> {Wh;U"YSh,I,. Triuu cteus Shales. / OJ Whittery Ash. Beds. i'" cri ro. lIIarrington Hagley Sh ale. IShale. Longville Flags. u ~ Group H agley Ash. Ashes and Lavas. Chatw.a l l or o:: f:3 Soudley Sand- o m I stones. . < ) Aldres s Shale. Criggion Shales . Harnage Shales. ....l 9. Spy W ood < Group I Spy Wood Grit. Hoar Edge Grits CO I and Limestone . I -_. I

SHEL VE OR A RENIG SERIES. The St iper Quart zite is much indurated and has it s sand gra ins remarkably well rounded. It has only yielded worm­ bur rows and doubt ful tr aces of Lingula. I ts outcrop forms a high moorland rid ge, from which considerable rock masses jut out, such as the Devil's Chair and Cranberry Rock. T he AIytton Croup consists of hard shales interbanded with gritty flags, the denudation of which gives rise to the character­ istic and interesti ng scenery of Mytton Dingle. In thi s di vision occur veins of lead and zinc, and also some barytes, both on the main outcrop and in the anticline of Shelve Hill. Ogygia selwynii and Obolella plu mbea are the chief f ossils in the mining ground, and in the upper beds near Shelve Church is a band vielding various for ms of Dichograptida ; Didym ograptus llirundo, and D . exte nsus have been found in the Mytton Group. The H ope Shales outcrop over a large area and are softe r and more monotonous in character. T hey yield few fossils, mainl y GEOL. Assoc. JUBILEE VOL. PLATE XXIV.

, 1'11010 by 11'. 11'. 11'11 1/$. FIG. I. - Q UARRY AT TASGAR : TH E STA1' ELEY ( UPPEl{ ARENI G) A SH-B ED, WITH FOSSILIFEROUS SHALE S AT T HE BASE (TO THE LEFT).

FIG. 2.-SECTIOI': AT H OP E RECTORY: CONTORT ED HOPE ( :.\cIIDDLE AR EN IG) SHALES. To[ace page 752. SHROPSHIRE. 753 graptolites, Didymograptus bitidus, etc., and the higher beds are interbanded with ash layers. Where cut deeply by the Hope Stream they form the bea utiful Dingle of that name tr aversed by the road from Min sterley to Bishop 's Castle." (Plates XXIV, F ig. z, and XXV, Fig. I.) The S tapeley A shes, like th e last division, are rep eated by th e Shelve Hill Anticline, giving rise to three hill ran ges, of which the most important is the Stapeley ridge with its continua­ ti on bv Llanfawr, the Roundtain, and Todleth. The Ashes are andesitic, water-deposited , a nd fossiliferous, frequ ently inter­ leaved with shales, and among them, where the prin cipal hills occur, are sheets of porphyritic augite- and hypersthene-ande­ site (Plate XXIV, Fig. I). Associated with the ash beds th ere is a considerable amount of intrusive dolerite, as at Ll anf'awr and the Giants' Graves.

MIDDLETON OR LLANDEILO SERIES. The lowest member of the Llandeilo division, the W eston Stage, consists of shales containing two beds of volcanic grit, in which fossils are scarce, but 0 gygia corndensis has been found. The Betton Shales, which yield abundance of Didymograptus murchisoni and Orthis are best exposed south -east of the village of . The 11lead owtown Stage is mainl y calcareous, consisting of fossiliferous flags and limestones, bearing Ogygia buc ftii and Asaphus tyrannus at the well-known localities of Church and Meadowtown. T fte Rorrington Shales, the high est division of the Llandeilo Series, is made up of intensely black mud stones and flaggy shales, in certain bands of which, about Spy Wood, are found large and beautiful specimens of Leptograptus flaccidus and N emagraptus gracilis.

C HI RBURY OR BALA SERIES. The highest beds of the black flags alternate with thin grits, which gradually become thicker and more important until the main mass of the Spy TV ood Grit is reached. This contains many fos sils, brachiopods, trilobites and graptolites, but the charac­ teristic fossil is perhaps B eyrichia complicata, The Aldress Shales are pale, barren, and monotonou s, bear­ ing a few graptolites, but with one zone extraordinarily rich in D ict vonema. The shal es are of very considerable thickness. The M arrington Stage consists of two beds of ash , mainly andesitic , with bands of shale between and above them. The group is traversed by the , which has cut out the

* Geol. Mog , dec . 5. v o], i, 1904, p. 2 10. 5° 754 GEOLOGISTS' AS SOCIATION JUBILEE VOLUME. beautifully timbered ravine of Marrington Dingle. The ash beds have been much quarried, and show pisolitic or spherulitic structures; they are sometimes ripple-marked and fossiliferous. Lavas of andesite are sometimes associated with them, and there are some bands of paler and more acid tuffs. Barytes is worked in the ashes at . The Whittery Shales are the highest Bala beds exposed west of the Longmynd; their meagre fauna is not distinctive. A narrow strip of Lower Bala rocks rests unconformably on Longmyndian rocks east and north­ east of Pontesford Hill, THE BREIDDEN HILLs.-In these hills the Criggion Shales may correspond with the Aldress Shales, which they closely resemble in their generally barren character, but the Dictyonema bed has not yet been found. The hills of Moel-y-Golfa and Middletown are scarps of ande­ sitic lavas, ashes, and boulder beds, among and above which have been found some of the fossils of the upper Glenkiln and lower Hartfell fauna. The volcanic group is closely overlapped by the local base of the Silurian. There are several sills and lacco­ lites of dolerite in this area, the most prominent being the im­ posing mass capped by Rodney's Pillar, which plunges westward to the Severn in a cliff a thousand feet high, the most striking feature to be seen anywhere on the Welsh border. THE CARADOC SANDSTONEs.-The Ordovician Rocks east of the Longmynd are markedly different from those to the west. In the first place, the Arenig and Llandeilo divisions are un­ known and probably absent; secondly, the floor of the Bala rocks is an unconformity; and, in the third place, the general facies of the rocks is a sandy, shallow-water type, with few shales, in place of the shales and ashes of the west. The basement bed, where its relations are not concealed by faulting, rests uncon­ formablv on various older rocks, Cambrian or Pre-Cambrian. At this bed can be seen in contact with the volcanic rocks there called U riconian, and fossils can be col­ lected from it as well as pebbles of the volcanic rocks; and in the old quarry at the south-east end of Hazler Hill fossils are obtainable from calcareous sediments washed into the fissures of the underlying igneous rocks in Bala times. The Hoar Edge Grits are conglomeratic grits with bastard limestones, rich in fossils, chiefly brachiopods, but with trilo­ bites also. The rocks, where they overlie the soft Shineton Shales, give rise to a considerable scarp at Hoar Edge, Grange, and Evenwood, but they are much less conspicuous when in contact with the U riconian or other hard rocks. The Harnage Shales are the probable equivalent of the Aldress Shale, with which they have many characters in common. But they yield rather more fossils, especially brachiopods. The list SHROPSHIRE. 755 given by Salter" is not reliabl e, as these shal es were not at that time differentiated from the Shineton Shales, a distinction that is due to Dr. Callaway. T'h« Cliatzoal! or So udle y S and stones are much quarried for building purposes. They are olive-green or brown in colour, of ten with purple streaks, and they yield brachiopods and trilo­ bites. These rocks may be regarded as the typical ,. Caradoc Sa ndstones" which Murchison clearl y had in view when he coined the name. The thin-bedded flags and associated sandy shales of CIteney l ongville are of great thickness. Many beds are richl y fossil­ iferous, yielding Phacops conophthalmus, and T enta culites all­ nulatus, but the most import ant band is one of sandy limestone

F IG. 117.- 'ECT IO:-l T H ROUG H IIAI{ :-lA ( ; ~; GRA:'> GE MID llIWO ~ I C I W FT. ­ C. Cat/arM)'. (Repri nte,1by perm ission 0/ tire Council a/ lite Geologica l S ociety .) (Qnart. jo,ml. Geol; Soc., \'01. xxxlii, p. 6SS.) ~ . s. Harnage Grange. Broomcroft, I I I

~ a. :'.lay-llill an dstone. d. Hoar-E dge Grits. b. Charwall . andstone. e. Shineron ' hale. c. Harnage Shales. near the ba se, which contains Trematis filosa, and, from the abunda nce of Orthis alt ernata in it, is generally known as the " Alternata limestone." Tlte A cton Sc ott Beds are dark grey shales with bands of con­ cretionary limestone. They are fossiliferous, and yield a number of corals. Some of the high est beds exposed are seen best in the well ­ known section on the Onny River. They are thin-bedd ed, sandy, yellow or grey shales, and from the abundance of Trinucleus con­ centricus are known as the Trinucleus Shales (see Fig. 128).

THE SILURIAN SYSTEM.

The Shropshire type of Silurian rocks, mudstones altern ating with limestones, is developed on the flanks of Wenlock Edge, stretching from the Severn at Benthall Edge to Ludlow and ' Qlta et . I ou rn . Geol , Soc. , \'01. x ( 1854), p. 64 756 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME.

beyond. But the Denbighshire type, flags and graptolitic mud­ stones, occurs also in the county, on the Long Mountain and in Forest. The two types may be contrasted in tabular form as follows: ------Wenlock Edge Area. Long Mountain. I~-----·_··- ..------Upper or Temeside Group. Passage Beds. LUDLOW Upper Ludlow Rocks. Cardiola Flags. Series. Aymestry Limestone. Hard Flags.

Middle or Lower Ludlow Rucks. lVI udstones and Flags. WENLOCK Wenlock Limestone. J Concretionary Series. Wenlock Shale. I Mudstones.

Lower or Tarannon Shale. Purple Shale. LLANDOVERY Upper Llandovery Rocks. Llandovery Sandstone. Series. (Lower Llandovery absent).

One of the most striking features of Shropshire landscape is­ furnished by the outcrop of the Silurian Rocks. This is Wenlock Edge, a double scarp, formed by the Wenlock and Aymestry Limestones. At Kenley the Llandovery Sandstone forms a third scarp line. The edge is only broken three times, by the Severn at the" straits" above lronbridge, by the Onny at , and by the Teme at Ludlow. Apedale, at the foot of the main scarp, is occupied by the Byne Brook and its longitudinal tribu­ taries flowing south, and the Shineton brook flowing north to the Severn. Hopedale is the discontinuous hollow at the foot of the Aymestry Limestone scarp, drained by a series of small subsequent streams, which turn and flow through the numerous transverse gaps cutting through this latter limestone, and join the River Carve. Corvedale is the long. strike valley draining the main south-eastern dip slope.

LOWER SERIES. The Lower Llandovery Rocks are not at present known in Shropshire, and the Upper Llandovery Rocks rest on older rocks with a flagrant unconformity. As the highest Ordovician rocks are absent as well, there must have been a cessation of deposition for a long period, occupied by earth movement and the extensive denudation of the rocks so disturbed. There appear to be also local gaps in the succession of the Silurian Rocks themselves, especially in the Wenlock Epoch, as though shallow water and intervals of minor denudation persisted. The basal unconformity is a very striking one, and is particularly well seen in the map of SHROPSHIRE. 757 the west side of the county, where the Pre-Cambrian, Cambrian, and Ordovician Rocks have been largely stripped of their former Silurian cover. In section the unconformity is deceptive and not easy to locate where it crosses the Onny River, but it is well seen in the Shineton Brook, the streams north of the Shelve area, and in Hope Dingle (Plate XXV, Fig. r). Tlte Upper Llandovery Stage. The basement conglomerate and grit, often fossiliferous, flanks the Cambrian east of the Wrekin. Sweeping south-west as a considerable scarp to Kenley and Church Preen, it lets one bed after another of the Ordovician out from beneath it until it comes to rest on the Trinucleus Shales, the main escarpment at the same time dying down. East of Cardington it rests on the Uriconian Rocks, and to the west and west-south-west covers the edges of the various members of the

FIG. I28.--SECTION ON THE NORTH BANK ON THE RIVER ON NY AT FOOTBRIDGE, SHROPSHIRE; SHOWING THE PENTA­ MERUS-BEDS LYING UNCONFORMABLY ON THE OLDER STRATA.- J. IV. Saltrr. (Rep , i" ted b)' perm ission 0/ the CCII "til 0/ the Geological Sotiel)'.)

[Qlla,t. [ ourn, Geo], Soc., vel. x, p, io .1

f. Trinucleus-shales (Bala rocks). i . Pentamerus-beds. .~~. Pur ple Shales, followed by Wenlock Sha le.

Longmyndian, Cambrian, and Ordovician sequence. Its most striking situation is to the south-west of the Longmynd, where it rests nearly flat against the steep western cliff of that plateau, doubtless an old sea cliff in Silurian times. A thin, fossiliferous, basal sandstone closely overlaps the Bala rocks of the Breiddens at Middletown and Buttington. The Pentamerus Limestone is a sandy, bastard limestone, with abundant fossils, chiefly P. oblongus and Stricklandinia lens, but Encrinurus punctatus and other trilobites may be found in it. It is well seen in Morrell's Wood, east of the Wrekin, to the east of Cardington, and at Norbury. Purple shales, the 'probable equivalent of the T'aranuon Shales, are widely distributed, but usually not well exposed. Fossils are uncommon, but Salter gives a list j most of them occur in the Wenlock Shale, while a few are Llandovery forms. Few graptolites have been found in the shales. 758 GEOLOGISTS ' ASSOCIATION J UBILEE VO LU M E.

MIDDLE S ERIES. T he Wenlock Shales are bluish-grey mudstones, generally barren, but with two or three beds very rich in admirably pre­ served fo ssils, especially minute brachiopods like Orthis biloba, Strept is gray a: , Glassia , and Dayia. Messrs. Maw and D avid­ son, * by means of th e brachiopods, broke the succession up into four divisions in ascending ord er : (I ) Basement Beds, (2) Build­ was Bed s, (3) Middle Shale or Coalbrookdale Beds, and (4) Upper Shale or Tickwood Beds (Fig. 129)' T he Wenlock Limestone is earthy and grey in colour, gener ­ ally occurring in small concretionary masses or thin bands mingled with shales (Plate XXV, Fig. 2), . but occasionally passing into large crysta lline masse s known as " ball-stones," very variable in size and once much quarried for iron-smelting. The thickness of the limestones varies very considerably along its strike, and with it the height and importance of the escarp­ ment. Fossils are extr ernely abundant, especially cora ls and brachiopods, but trilobites are scarcer. The extreme rarity of graptolites renders exact correlation with the graptolitic zones of the Denbighshire type of Wenlock Rocks quite uncert ain. In the Long Mountain, Miss G. L. Ellesj has shown that four of th e six graptolite zones of th e Wenlock Shale group are pr esent, the first and third from the bottom being absent or unrecog­ nisabl e. The zones are in ascending order: (I) Cyrtograptus murc hisoni (absent ) j (2) illonograptus riccartonensis ; (3) Cyrto­ graptus symmetricus (absent) j (4) C. linnarssoni , (5) C. rigidus : (6) C. lundgreni. T he shales and limestone of the Wenlock and Ludlow areas cannot yet be correlated , but presumably th e highe st zone is about equivalent to the Lim estone. The L ower Ludlow R ocks are closely linked with the Wen­ lock Limestone in their f ossils and with the Wenlock Shale in their colour and lithology. Many beds of the mud ston es are richl y fos siliferous. Miss E . M. R . Wood (J\lrs. Sh ake spear }; divides the graptolite-bearing Lower Ludlow Rocks of Ludlow into four zones, in ascending order: (I) ill onograptus nilssoni; (2) M. scanicus " (3) M. tumescens ; (4) M. leinttuardinensis, The upper half, amounting to 275 feet, of the last zone is composed of the Ayrnestry Limestone, which would be classed by th e writer with the Lower Ludlow Beds. Miss Wood recognises in the Long Mountain a zone, th at of Monograptus vulgaris, lower than those occurring in the Ludlow district j the zone of M. nilssoni is there provisionally divided by her into the subzones of M. nilssoni and M. rcemeri , and the type fossil of the highest zone is represented by M. leintiuardinensis

:t Ge ol. Mag., de c. 2, vol , vii i ( 1881), pp. I, r oo, 145, 289. t Qua rt. [ our n, Geol . Soc., v·0 1. Ivl (1900). p- 370. ~ Quart. [ ourn , Geol . Soc. , vol , l vi ([900) . p . 4 . '5 GEOL. Assoc. JUBILEE VOL. PLATE XXV.

[Photo by W. '·V. Watts. FIG. I.-SECTION IN HOPE DINGLE: HOPE SHALES AND ASH-BEDS (MIDDLE ARENIG) IN FOREGROUND, LLANDOVERY SANDSTONES IN BACKGROUND.

[Photo by W. W. Watts. FIG. 2.-RoAD-CUTTING THROUGH WENLOCK EDGE, W. OF MUCH WENLOCH, SHOWING WENLOCK LIMESTONE. 1'0 face page 758. cr­ V) .... FIr.. 129 .- S ECTI ON ACROSS T il E SIl .1JRIAN STRAT ,\OF SIi ROrSJlIRE .-Afilr C. ,lI t/1/).

( r;eol. .lIne., dec . 2, vel. viii, P. loG.] :\ .:\ .\\'. S.S.E. Jk-uth.•11Ed;.:.· ;11l,1 Stolle n ee-e. lluildwas A1tlJC)" '\ \ :III,-".:L; Etlh" " Unl>(''il.llr. I .illk) Bruuk,

:'ol.·rri..h l.. a IlC·30Rout,:h. c'orvcd.uc, \r ,N,.1. "lt u;h \\ "':1110(;". " Iw.t lle. (:v.,lllfoukd...lc, H ark )", Uur ton . ,. O.R.S

~ ~ " ~ lil : ~, ~ ~ :I ~":~ I P: ~~ ..". ~ :~\ ._ .. ,,-:::::-:-r-. ~-.>--~ -l,,'~ .... " - ..L-' ~ \ s= __~ _""' - ::::-J '

~ ~. ~~~~~~ ~~~-{f:';J:-r. :-~~ '& 'i."" ,,/.,... '-"-iw " , -, e - l - ~.,~ ~~'i--o; ~'----0:~-- o '-' ~ - - .,;::------tl ,. .... t , ... . u· Co I ."c. -f' ,," c "; "· I., ... .(. _ h •• _ \ ..... Cl( t o .• • - T":"':---, ~ 1 Z I.~ i : ,"': .t:~ hi /; c I ,.('1 1. h J 11/

c Shinct on Shale s. hZ Build was Beds. j: Shale s over Limestone, I H oar Ed~cG rit . h~Coalbrookda le Rc

,f!~ Lime stone. hI Tickwood Bcds I (j ppcr Ludl ow, hi Basem ent Beds U. W enlock S hale. 11/ I'a ssa ce Beds, I.. W enlock Shale, i\ W en lock Limestone, a .N.S. 01<1 Rcd Sa nd stone.

Tlu l ort//ilia are 1101till 011Ihl StllIII /illl t>fSection. 110I'i::oll lll/ Sm/" I illrh = 1 mil«, 76 0 GEOLOGISTS ' AS SOCIATION JUBILEE VOLUM E.

var. incipiens, the type itself not having hitherto been recorded from this localitv. The last zone consists of hard calcareous flags, which mayrepresent the Aymestry Lim estone.

UPPER SERIES.

The Aymestry Limestone is lithologically much like the Wen­ lock Limestone, and cont ain s many of the same coral s and brachiopods. It is also very variable in thickness and is some­ times spl it into several bands. Its type fossil, P entamerus (Con­ chidium) kni ghtii, is, however, only locally common. It is generally altogether absent, but where it does occur, as at Mock­ tree and at Weo E dge, near Craven Arms, it is very common, and at the latter locality it is present in thousands, a thickness of twenty feet of rock being entirely composed of the shell. Miss Elles and Miss Slater" place in the Aymestry Group the suc­ ceeding Mocktree Shales and thin limestones cha racterised by the abundance of Dayia navicula. The Up per Ludlow R ocks are usually sands tones, sometimes arg illaceous and at other times calcareous. They are typically seen at Whitcliffe, near Ludlow, and are divided by Miss E lles and Miss Slater into a lower division, the zone of Rlsynchonclia nucula, and a higher zone of Chonetes striatula, The highest band at Ludlow is the fam ous bone-bed, a lay er with the colour and consiste ncy of gingerbread , an inch or two in thickn ess, full of fragments of fish bones, scales, and spines, with worm-tubes an d bits of crustacean tests. This bed has been recognised near Bishop's Castle, 'at Diddlebur y, and at Linley Brook j but it is typically seen at Ludford Lane, near Ludl ow, an d at Norton Camp, above . The T emeside Group includes a lower division, the yellow building sandstones of Downton Castle, which forms the zone of Lingula minima, and an upper divi sion, the T emesid e Shales, the zone of Lingula cornea and Eury pterus, Each of these divi­ sions contains a bone-bed or its equivalent. I n these remains of Ostraco derrn and Acanth odian fishes are not uncommon, Cya­ thaspis, A uchenaspis, Eukeraspis, and Climatius being charac­ teristic genera. I n the Long Mountain the Upper Ludlow Rocks are repre­ sented by a considerable thickness of ftaggy beds and cardboard­ like shales containing few fossils except Cardiola interrtcpta. The summit-beds of the syncline are mapped by the Geological Survey as Old Red Sandstone, and at their base occurs a band swarming with Ling ula cornea. Probably these rocks are homotaxial with the T emeside group. "Quart , 1Du rn. Geol : Soc., vol. lxi i (1906), p . '95. SHROPSHIRE.

OLD RED SANDSTONE. The Old Red Sandstone covers a large area in Shropshire. It succeeds the uppermost Silurian Rocks conformably along Corve­ dale. It was visited by the Association in 19°4, under the direc­ tion and presidency of Dr. A. Smith Woodward, who has been kind enough to give the appended notes on it and on the bone­ beds mentioned above. T Ite Lower 111ember is composed of alternating red and green sandstones and marls with bands of impure, concretionary, un­ fossiliferous limestones, known as cornstones. The last rocks frequently form escarpments like those ranging round the Clee Hills, making the base on which these hills are built. The only fossils are remains of Eurypterids and fishes, and these are usually rare. The characteristic fishes are the Ostracoderms Pteras-pis and Cepltalaspis, and an Arthrodire Phlyctanasois, T he Upper Division is the quartzose conglomerate and sand­ stone series of Murchison. The rocks are well seen on the lower slopes of the Clee Hills, and a yellow sandstone at Farlow has yielded fish-remains. Bothrioiepis has been found here in asso­ ciation with scales and teeth of a Rhizodont Crossopterygian, perhaps Sauripterus. These fossils represent a horizon equiva­ lent to the uppermost part of the Scottish Old Red Sandstone.

THE CARBONIFEROUS SYSTEM. The Carboniferous System in Shropshire is found in five distinct areas, three of them of Midland Type, one, perhaps, of Southern Type, but the fifth, that of Oswestry, is of Pennine Type, and has been referred to by the late Mr. Lomas* in his account of the Berwyn Hills. The other four are the coalfields of Coalbrookdale, with and Dryton, the Forest of Wyre, and the Clee Hills. In all these areas the Lower Carboniferous rocks are absent or imperfect, and even the appearance of conformity at the base of the Titterstone Clee rocks about Farlow and Hope Baggot is probably deceptive. Elsewhere the basal rocks rest unconformably upon Old Red Sandstone, or more usually on older rocks. A representative of the Carboniferous Limestone underlies part of the Coal brookdale and Titterstone coalfields, and so-called Millstone Grit is present also, overlapping the Limestone towards the south in the former case and towards the north in the latter. Between the two extremes Coal Measures overlap directly on to older rocks, and the higher members of this Series overlap the lower. In the Coalbrookdale coalfield a strong unconformity occurs below the Upper Coal Measures, the Lower and Middle Measures having been submitted to an interval of movement and denudation. This

"Proc. Geol, Assoc., vol. xx (1908), p. 477· 762 GEOLOGISTS ' ASSOCIATION J UBILEE VOLUME.

phenomenon, known previously as the Symon " fa ult, " was rightly attributed to denudati on by Scott* in 186 I, but the add itional influence of intra-formati onal movement was detected and explained by Mr. Clarke] in 1901. This author also infers the extension of these relations into the Forest of Wyre and Clee H ill coalfields. T he Carbonif erous l im estone of the Titterstone Clee is stated by D r. Vaugh an ! to belong to the zone Zz , and as the beds con­ taining the fossils of thi s zone are closely succeeded by grit bed s, the " ilf ill stone Grit " conditions here must have begun very earl y. The Limestone of the H atch near Wellington is placed by Dr. Va ughan in the Dibunophyllum zone, and it is separated fr om the und erlying Cambrian and Silurian Rocks by a sill of dolerite. Little work has been published on the Coal Measur es since Prestwichss classic paper was written, but the succession appears to fall roughly int o line with that established by Dr. Gibson in other Midland coalfields. The lower measures contain a few coals j the middle or grey measures are productive, and yield several seams of coal and iron stone, with clay much used for brick-making and pottery, the chief industries of Jackfield, Coalport, and . Then comes the unconformable upper division, with thin (and " stinking") coals and Spirorbis limestones. One may hazard the conj ecture that thi s di vision is parall el to the Newcastle and H alesowen sandsto nes. Then foll ows a first division of the red rocks form erl y considered as P ermian, and mapped as such by the Geological Survey, but called by Mr. Cantrill] "Coal Measure P assage Beds," because their stratigraphical relati on­ ship to the Carboniferous is close, and they contain Spirorbis limestones and thin coal seams. This divi sion appears to cor­ respond with Dr. Gibson's Keele Series. Mr. Cantr ill, how­ ever, cannot separate this lower division from the " Mid dle and U pper P ermian " of Mr. Wickh am King, to be shortly referred to, and would call the whole three divisions " P assage Beds."

THE "P ERr'MAN" ROCKS. The Red Rocks of the lower Severn Basin, formerly coloured on the Survey Maps as P ermian, are thus divided by Mr. King:~ 3. Upper Marls with included breccias. 2. Middle Group of calcareous sandstones locally con­ glomeratic. I. Lower Group of marl s and sandstones.

>\< Quart. [ourn, Geol. S oc., vol. xvi i (1861), p . 457. t Quart. [our n, Geot, S oc., vol. Ivii (190 1), p. 86. t Quart. [ourn, Geol . S oc., vo l. l x i ( 1905), p . 252. § Trans. Ge ol . S oc. , series 2, vol. v (1840), p. 413. II Qu a rt . 1 0UT1l . Geot , Soc. , vo l. Ii (1895) , p. 547- 'If Qu art. 1 0 1l T1/ . Geo l : Soc., vo l. I v (1899), p . 97. SHROPSHIRE.

The lowest division has already been referred to as probably equivalent to the Keele Series of North Staffordshire. The middle division shows, near Enville, at Alberbury, and elsewhere, calcareous conglomerates, at times dolomitic, the pebbles having been derived from older limestones, chiefly of Silurian and Carboniferous ages. The pebbles appear to be somewhat local in origin and not to have travelled far, as Mr. King is able to recognise local varieties in situ in their neighbour­ hood. The great breccia (the "trappoid breccia "), the most con­ spicuous member of the upper division, is made up chiefly of angular fragments of Archaean rocks. At first considered to be of volcanic origin, and then attributed by Ramsay to ice-trans­ port, this breccia has been held by others to be made chiefly of scree material produced by denudation, etc., of local Archrean masses. The other Permian rocks are of the usual Midland type and call for no special remark.

THE TRIAS. The Trias of Shropshire falls into the usual divisions, the "Pebble Beds" forming a very conspicuous member of the Bunter. This division stands out as a strong scarp east of the Severn near , and the protection afforded by it has given rise to some very beautiful scenery where this river cuts into the Lower Mottled Sandstone. Hard beds at the base of the Keuper also give rise to the charming scenery of Nesscliff, Grinshill, and Hawkestone, and to scarps, more or less repeated by faults about Albrighton and . Much of the north plain of the county is based upon Keuper Marls, frequently covered deeply with superficial deposits. At Grinshill the rocks have yielded tracks and bones of Rlzync1lOsaurus.

THE JURASSIC SYSTEM. In the middle of the northern plain, between and Audlem, there is an outlier of Rheetic Rocks not less than 10 miles long. It is covered by Lower Lias and a small patch of Marlstone. The zones represented extend from that of Ammon­ ites planorbis to that of A. jamesoni.

THE PLEISTOCENE DEPOSITS. Much of the northern plain is overspread by drift, part of it being boulder-clay. The northern and eastern sides of the county also show a vast number of boulders, doubtless once con- 764 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME. nected with drift deposits. These are especially prominent near Wellington and Eaton Constantine, and about Bridgnorth. They consist chiefly of Scottish and Lakeland rocks, such as the Criffel and Eskdale granites and the lavas and tuffs of Borrowdale. There are also many blocks of Welsh felsites and andesites, mainly from the Arenig district, belonging to a different dispersal. The great Northern ice-sheet, moving from North Wales and the Irish Sea, does not appear to have over-ridden the higher parts of the Longmynd. Its characteristic northern and north­ western erratics, granites, felsites, etc., are however abundant in the lower grounds to the north of the Longmynd. They are met with also on the flanks of the Stretton valley to the east, occurring as far south as the town of Church Stretton itself, to the south-west of which they are frequent in the gravel terraces on the western slope of Ragleth Hill, at a height of between 700 and 800 feet above sea-level. South of the crest of the Longmynd-Shelve upland area such erratics as are met with indicate the presence in glacial times of a more southern ice-sheet or ice-lobe, moving from west to east from the Mid Wales region of Plynlimmon and the Upper Severn, south of Montgomery and the Longmynd Uplands, towards the valleys of the Lower Onny and the Teme. The picrites of Cefn (1,000 ft. O.D.) have been carried north-east­ wards to a height of 1,150 feet in the Shelve country, and the ashes and dolerites of the Corndon area, eastwards to still greater elevations in the south-west parts of the Longmyndian area. Illustrations of the characteristic physiographical phe­ nomena usually regarded as related to the advance and retreat of the ice-sheets of the Glacial Period, are by no means uncom­ mon in the Shropshire uplands suggestive of dry overflow channels (Golden Valley), dry marginal channels and cut-offs (north of Church Stretton); there are also gorge-like valleys (Marsh Brook, etc.), and diverted stream courses (south of Church Stretton-that of the oxbow-like valley west of Brock­ hurst is a conspicuous example). The low-lying grounds north of the Longmynd are overspread with glacial drift, gravels and sands rising now and again into long moraine- or esker-like ridges of great height and length. These drifts rise on the north-eastern flanks of the Longmynd to heights of nearly 900 ft. above sea-level, and in the branches of the Smethcott Brook appear to be locally more than 50 ft. thick. Sands and Gravels, sometimes with marine shells, occur about Ketley, , and at Gloppa, near Oswestry. At the last locality* they range from 900 to 1,160 feet above sea-level, yielding marine shells up to I, I 20 feet. Just at the mouth of *Quart. [ourn. Geol. Soc., vol. xlviii (1892), p. 86. SHROPSHIRE. the Severn gorge, at Buildwas and Strethill, Mr. G. Maw" described similar sands and gravels bearing northern and local boulders and yielding 4I fossils, mostly marine shells. North­ west of this locality numerous gravel ridges, with the appearance of eskers, are found, often enclosing land-locked hollows, once the site of lakes. Relics of larger lakes, like that of the . are also found in the north j and the large meres about Ellesmere and the myriads of tiny pools east of Whitchurch are doubtless relics of a time of lakes, which, in the county, fol­ lowed the Glacial Period.

THE IGNEOUS ROCKS. Space will not permit of any lengthy treatment of the igneous rocks of Shropshire.

INTERBEDDED ROCKS. The contemporaneous volcanic rocks have been claimed as Uriconian and Ordovician in age. The first are rhyolites and andesites, associated with agglomerates and tuffs. The second are basaltic andesites, bearing hypersthene or augite. It is often a matter of no little difficulty to determine whether some of these latter are lava flows or shallow intrusions. The associated tuffs are of identical composition and contain fragments indis­ tinguishable from the andesites in sita,

INTRUSIVE ROCKS. There are at least four distinct groups of intrusive rocks: (I) Those intrusive in the Uriconian areas j (2) the post-Cambrian carnptonites j (3) the Ordovician and Silurian hypersthene­ dolerites and associated rocks j and (4) the post-Carboniferous olivine-dolerites. (I) Uriconian areas.-The first group ranges from aplites and granitoid rocks, the only abyssal rocks in the county, to intrusive rhyolites and andesites. Associated with these are innumerable basic rocks, mainly dolerites, the majority of which were olivine­ bearing. This group of dolerites probably also includes some of those intrusive in the Longmynd, but mixed with them in both areas are almost certainly some post-Carboniferous dolerites. (2) T'he camptonites are almost the only hornblende-bearing rocks in Shropshire. They are at present only known as a few dykes in the Longmynd and as an intrusion into the Cambrian on the east of the Wrekin. The rocks are allied to the sills of the ~uneaten districtt and to similar rocks intrusive into the Highland Cambrian rocks of Inchnadamff. t '" Quart. [ourn. Geoi, Soc., vol. xx (1864), p. 130. t Proc, Geo!. Assoc., vol. xv (1897), p. 394. l Ceo! Btag., dec. 3, vol. iii (1886), p. 346. 766 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME.

(3) Ordovician and Silurian intrusions.-In the Breidden and Shelve areas there are innumerable intrusions of hypersthene­ augite-dolerites, a little more basic than the andesites, and with­ out olivine or hornblende. They are certainly intrusive, occur as sills, dykes, and laccolites, and sometimes, as at Corndon, form very considerable masses. They occasionally come into contact with Silurian rocks, and there is evidence that they may range in age from Ordovician to Silurian. They seem, however, re­ lated in composition, and possibly source of supply, to the Ordo­ vician andesites. They are probably not confined to Ordovician areas, but may have furnished some of the intrusions into older rocks, like the Longmyndian and Uriconian. Restricted, so far as known, to the Shelve area is a set of augite-picrites such as those of Cefn, near Corndon, fragments of which cover much ground at Dysgwylfa and Shelve Pool. (4) T'he post-Carboniferous olivine-dolerites which are best known are the sills capping the Titterstone Clee and the two summits of the . Here they are intrusive into the Coal Measures, as they are at and Little Wenlock, but a precisely similar sil( is intrusive below the Carboniferous Limestone of the Hatch, coming between it and the Shineton Shales. They have not been seen in contact with newer rocks, though in Staffordshire exactly similar rocks cut the Permian and the Bunter Pebble Beds. The rocks are well-preserved olivine­ dolerites, indistinguishable in their lithology, as Allport showed, from the Tertiarv rocks of Antrim and West Scotland. It is more than likely that these rocks are also Tertiary in age. Some of the olivine-dolerites piercing the Longrnyndian and Uriconian rocks are most probably of the same age. These olivine-dolerites are highly valued for road-metal and constitute the well-known "dhu-stone" and" Clee Hill granite." It will be noted that the county is free from the Old Red and New Red Sandstone volcanic rocks and their accompanying plutonic masses, and that there are no contemporaneous volcanic rocks of Carboniferous age.

TECTONIC GEOLOGY.

FOLDS, FAULTS, AND INTRUSIONS. In Western Shropshire the dominant trend of the rocks and of their folds and faults is from north-east to south-west­ namely, that especially characteristic of the Caledonian move­ ment j not only in the older rocks, but in the New Red Sandstone and Lias. This leading trend is largely followed by the pro­ found north-east and south-west fault which sweeps through the county from Lilleshall, through Church Stretton, to Radnor. Judging by the rocks in contact with it, this has been a line of SHROPSHIRE.

movement more than once, up to Triassic times, and even later. Part of this fault is the western boundary of the Coalbrookdale coalfield, to the immediate west of which no Coal Measures have so far been discovered. Passing westward across the Longmynd the trend gradually becomes more northerly in the pre-Silurian rocks, and this is very pronounced in the Ordovician, in the Shelve Hill and Corndon anticline, and in the anticlinal fault of the Severn valley west of the Breiddens. The major trough of the Long Mountain, however, which is formed of Silurian rocks, again presents the characteristic north-east and south-west trend, and is aligned with the axis of the Lias syncline of Wem. The same trend is shown by the Ludlow saddle, the synclines of the Brown

FIG. 130. -S ECTIO~ ACROSS T HE CORI'DO:\ L ACCOLlTIC :\IASS.-C. l a/ worth and 11'. IV. Walts. :\.\V. : .E.

d ~ :\Iy tton Flags ami Hope Sha le Gro up, nltercd at junct ion with Dolerite D. .13 Stapeley Ashes and Andesitic Lava of Llau fnwr,

Clee and the Titterstone Clee, and the smaller parallel folds visible in the recurrence of the Aymestry Limestone near Willey and in a boring north of Bridgnorth. The minor folds of the lower Coal Measures detailed by Mr. Clarke trend east-north-east. Along the Severn valley and to the east of it the trend again becomes more nearly north and south, as shown by the strike of the rocks, the eastern boundary fault of the Coal brook­ dale coalfield and the faults repeating the Pebble Beds. There are innumerable minor faults and folds, usually con­ forming to one of the two directions, amongst which it is only needful to notice the striking pair responsible for the Permian strip, with its core of Longmyndian rock, at Haughmond, which stretches north-east from Shrewsbury, the Charlton-Wrock­ wardine branch of the Wrekin fault, and several faults in the coalfield. Faults running at right angles to the dominant direc­ tion are numerous, but less important in their effects. The position of the igneous rocks has been found closely related to both folding and faulting, especially in the Shelve 768 GEOLOGISTS' ASSOCIATION JUBILEE VOLUME. region, where the Ordovician and Silurian rocks differ in trend and the Corndon laccolite was intruded in the core of the main anticline, and the innumerable sills and dykes follow lines of faulting or of discontinuity resulting from torsion. The chief periods of movement appear to have been the fol­ lowing: Post-Longmyndian, Post-Ordovician, Post-Devonian, Coal Measures, Post-Carboniferous, and Post-Liassic.

PHYSIOGRAPHY. The whole of Shropshire, with the exception of a few square miles in the north, is in the basin of the , so this river presents the chief physiographic problem in the county. Its course is divided into two very distinct parts at the" straits" just below Buildwas and above . Above this point the Upper Severn is practically at base level, and in its gradient, its windings, its deposits, and its relations to tributaries, presents all the characters of a mature stream. At this point it plunges into a narrow gorge quite youthful in aspect, with very abrupt sides, running from Ironbridge to Bridgnorth. Below the first town the valley is steeply V-shaped for a long distance, and the tributaries all occupy similarly steep and narrow gorges near their infall to the main stream. These relations are admirably shown by the run of the roo foot contour-line and are felt by all roads crossing the river or its tributaries. These phenomena have been theoretically explained by one of the writers (Prof. Lapworth*) as follows: The present Upper Severn, with its tributary, the Vyrnwy, was in pre-glacial times one of the headwaters of the Dee, and flowed northwards. Dammed back by the Northern and Welsh glaciers and ice­ sheets, the ponded waters overflowed at the lowest notch, which happened to occur in the continuation of Wenlock Edge to Lincoln Hill, at Ironbridge. In this notch there may have been originally the sources of two small streams, one on each side of the watershed j namely, a small Dee tributary flowing north­ westwards, and another small stream flowing south-east, towards Bridgnorth, near which it joined the River Worf, at that time the main stream of the pre-glacial Upper Severn. The north­ western water, diverted across the Ironbridge overflow, began to cut the notch deeper until, in the course of time, it was deep enough to drain off from the Dee basin all the waters of the present Upper Severn and its tributaries, and in this way much of the pre-glacial Upper Severn became transferred into the present Middle Severn. The increased cutting power due to the enlarged volume of water deepened the whole of the course of the present Middle Severn, and this, reacting on all the tributaries, caused them in like manner to cut their valleys back. Thus was

"Proc. Geol, Assoc., vol. xv (18g8). P' 425. See also F. W ..Harmer, Quart. fount. Geol. Soc., Ixiii (1907), P' 477· SHROPSHIRE. produced the marked relief which characterises the "Severn Gorge" and the lower parts of all its tributaries below the "straits," while the slow cutting of the gorge has not yet ad­ vanced far enough to quicken the sluggish stream above Iron­ bridge, which, as already pointed out, had attained nearly to base-level before the Glacial Epoch. This theory accounts also for the anomalous course taken by the Severn and its remarkable swing from a north-east direction to one south-east and southerly, and explains the character of the watershed separating the Severn waters from those of the Dee about Oswestry and Whitchurch.

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