123

LONG EXCURSION TO THE .

AUGUST 7TH TO 17TH, 1920.

REPORT BY J. FREDElUCK N. GREEX, B.A., F.G.S., Director o] the Excursion. PLAn: 5. OWI~G to difficulties of accommodation the excursion, originally planned to include visits to the southern part of the Lake District, had to be restricted to places readily accessible from Keswick. While the glacial geology, physiography and minerals were not neglected, the chief object was to examine questions of vulcanicity, sequence and structure. The main controversial points were enumerated by the Director at an evening meeting on August 8th, when he gave a brief account of the points on which his 'views differed from those of earlier investigators. The foundation of his case lav in the identification of the .-, flow­ breccia'S," as lavas instead of tuffs or agglomerates, since this was the basis of his mapping. In this way he had arrived at a sequence in the volcanics, which had so far proved effective wherever applied. The larger part of this sequence was repeated ten times between Keswick and Coniston, so that the maximum thickness of the Borrowdales was probably only about 3,500 feet. This major folding was accompanied by concertina folding, especially in the softer rocks, in which the folded sheets often tended to horizontality. The Devonian folds were arranged fan-wise about an anticlinorial axis through Scawfell and the south of the mass. Working along these lines he had come to the conclusion, contrary to that of the Survey and the Cambridge School, that the upper and lower junctions of the Borrowdale Series were, as a rule, unfaulted, the volcanics resting conformably on the Skiddaws and being covered with a strong unconformity by the Bala Coniston Limestone series. Identify­ ing the unconformity in the north and correlating the Beds with the basal Bala, he held that the folds of largest ampli­ tude were Ordovician. Finally, considering the relations of the intrusions to these structures, he believed that practically all, with the exception of the Shap Granite and certain dykes, were pre-Upper Bala in age. AUGUST 8TH. DERWEXTWATER AXD FALCON CRAG. THE party walked to Castle Head, overlooking Derwentwater. From the top the Director pointed out the main elements of the geology; the Slates; Borrowdale Volcanics; intru­ sions; drift and alluvium; and drew attention to their effects on the scenery, notably the differences between the sediments PROC. GEOL. Assoc., VOL. XXXII., PART 3, IQ2I. 9 J. F. N. GREEN, and volcanics; the truncated spurs; the drumlins; and the division of the former Derwentwater-Bassenthwaite Lake by the Greta delta. Castle Head, composed of a dolerite, was generally supposed to be a plug, but he regarded it as a sill or thin laccolith, lying nearly horizontally. The surrounding slates had, however, high dips, so that the intrusion, if related to the Borrowdalcs, must be in an area of low sheet-dip. This and other points were illustrated on the published six-inch geological map ( (4). The dolerite, which had been described by Teall" and others, resembled the ordinary quartz­ hypcrsthene-dolerites found among the volcanics, but differed in containing a notable amount of biotite. Professor Schwarz suggested that this might be due to absorption of shale, as in South Africa doleritcs contained biotite when intruded among shales; and the Director agreed that the distribution in the Lake District supported this view. The accompanying metamorphism was slight, so that the thickness of dolerite could hardly be great. Proceeding by the lake to the base of Falcon Crag, an andesite lying below the" great purple breccia" was seen. It was un­ known to Ward, but may not have been exposed in his day. Some time was spent on the breccia and then a rough walk was taken by exposures of the bedded tuff" d " and Ward's" No. I lava" to the line where" 1'\0 2 lava" passed upwards into"f ash." The Director explained that this so-called ash belonged to the commonest type of flow-breccia of the Lake District, found plentifully everywhere, and that he regarded it as the crust of No.2 lava. He demonstrated the peculiar weathered surface in which the enclosed fragments yielded more readily than the matrix, giving a net-like face, the strands of which had a lacy appearance. In this instance the difference between the com­ ponents is not great, though visible on a freshly broken surface. The party then scrambled to the top of Falcon Crag. The summit consists of amygdaloidal augite-andesite, which shows some flow-brecciation in places and had accordingly been mapped by Ward as an ash, "i." About 150 yards. south, however, it was seen to be highly flow-brecciated with a marked difference between the components, the matrix being much the harder and weathering white. The Director regarded "j," a bedded tuff, as equivalent to his Middle Tuffs, though he had not yet proved it by mapping; and he thought that" l " might be a thin representative of the Harrath Tuffs, so that in Ward's type-section] the whole volcanic sequence would be present with the exception of the rhyolites. These, however, come in along the core of the syncline at Rigghause End, north-east of the foot of Thirlmere. On the way home, which passed by Walla Crag and Rakefoot,

• Rdtish Prfrot,rllph". p. 224. tGeology 01the North em Part 01Ihe English Lake District, plate v, LONG EXCURSIO~ TO THE L.\KE DISTRICT. 125 the Keswick stone circle was visited. A rectangular inner enclosure, now usually considered to be the remains of a fenced harrow, aroused much interest.

At;Gl:ST 9TII. CARRICK , THE DHY GILLS A~D SILVER GILL. ON arriving by motor at Mosedale, the party saw successively from south to north on the hillside (I) contorted Skiddaw silt­ stone, (z) the approximate position of the fault between the siltstone and the granophyre, where the rocks became almost indistinguishable, (3) the actual junction of granophyre and gabbro, (4), a small quarry at the junction of gabbro and con­ tact-altered andesite from which a remarkable strontium-bearing mineral had recently been described byMr. Melmore* as a variety of pectolite. The motors then went on, between crags of gabbro and the remains of an old lake, to Carrick Beck, where the position of the gorge at Linewath across the pre-glacial water­ shed, by which the lake had been drained,t was pointed out. The Dry Gills were reached on foot. On arrival the Director gave a historical account of this remarkable enclave and explained his view that the Bala shales with their accompanying rhyolite and dolerite had been dropped between two reversed faults, running east and west. The northern of these was plain, being filled by a big ore-bearing vein, easily traceable; the southern, which brings granophyre over Bala shale, was seen in the south fork, where the fault-breccias were readily found. Professor Fearnsidcs noted marked kaolinisation in the shales and drew attention to a hrematitc-staining connected with the fault; and, following this clue, convinced the Director that he had under­ estimated the hade of the southern fault. Time was then devoted to the collection of fossils, Trinucleus, Ampyx, Orthis, etc., and of minerals, Quantities of kampylite and pyromorphite were found accompanied by wad, barytes, chalcopyrite, malachite, etc. The party then steered across heathery moors at a height of z.ooo feet to the head of Silver Gill, where the gabbro, andesites, Skiddaw Slate, and polygenetic grit (Watch Hill Beds) could be seen near one another. At first sight there seems to be a regular succession downwards from grit through thin dark slate to ande­ site, all dipping at a high angle west-north-west ; but the latter part of this succession is clearly inverted, participating in the general overfolding which, along the northern strip of volcanics, is usually from north-north-west, but swings round to west­ north-west along Silver Gill, apparently owing to the obstruction of the Carrick Fell complex. Thus the position of the grit pre­ sents an extraordinary anomaly. At first sight the obvious 'interpretation is a fault between the slates and volcanics, bringing

"Geol, ~fag~, IQ:20, p. 266.. plarr, Geol, Mag., 1895, p. 300; I26 J. F.S. GREEN, up inverted beds lower than the main Skiddaws ; but th e presence of such fossils as Didy mograptus hirundo close to the grits in Ellengill on the west of Grea t Sea Fell, appears to negative this solution. And the mapping of the Surv ey, which the Direct or had verified, shows that the grits of Silver Gill are at the edge of a capping- of grit t o Great Sea FeU, underlain evcrwhere by Upper Skiddaw Slate. Th ere seem to be only tw o possibilities left; firstl y. that the grits ar e pre-Ordovician, pushed over the Skidd aw Slate and volcanics by an enormous thrust, or secondly. that they lie unconformabl y on the Skiddaws and have been folded up with them. Th ere is no known evidence of the former. and the latter view is supported by the composition of the gri ts, which are derivable wholly from the lower palieozoic rocks now exposed in their vicinity, and by th e nature of th e exposed junction with the slates. Th e apparent anomaly in th e sue-

NW

FIG. IS.-DIAGRAMM ATIC S E CT IO :-I ACROSS SILVE RGILL. cession at Silver Gill can be explained by the foldin g, as in the diagram (fig. IS). A UGUST IOTH. THE MELL A)< D EVCOTT HILL. AFTER leaving the train at Troutbeck the party paused near the Station to see the sha rp bend of the Trout Beck into its gorge, due to glacial diversion,* the brick pits in alluvium at the head of an old tarn along the beck 's pre-glacial course, and the mann er in which the stratification of , dipping at 120 to the east, was marked out by vegetation. On arrival at the large exposure of red breccia-conglomerate on , it was found that the weather precluded any good view of , but the Director pointed out the distribution of the Borrowdales and Skiddaws, which he considered conformable, in the ar ea north of the lake, and

·Warr., Grol. M~g.• 189,,1'. 3 0 0. LOKG EXCURSION TO THE LAKE DISTRICT . 127 c ommented on the dubious nature of the boundar y of the red conglomerate, which might be a fault or might only be oblique to the strike of the later beds through the wedging-out of sloping masses of detritus. The section shows a thickly-bedded series of coarse variable red breccia-conglomerates, with boulders up to a yard in length, almost entirely composed of Silurian .. Con­ iston Grit ," but with occasional lumps of limest one, polygencti c g rit, and igneous mat erial. Th e Director was anxious t o obta in the opinions of those conversant with tropical conditio ns, and interesting remarks were cont ributed by Mr. A. E. Kitson, who considered the conglomera te similar to those produ ced on land by torrential action with in te rcalati ons of ordinary river-gravel, t hus confirming Mr. K D. Oldham,* and by Professor Schwarz, who compared it with 'parts of the Enon conglomerat e. Mr. Green then gave his reasons against the views of Good­ child, who derived the boulders from the south of Scotland, an d of Ward, who thought they cam e from the southern Lak e Dis­ trict; and for supposing them to have been washed down from a Devonian mountain formerly occupying a situation ncar Skiddaw and Saddlcback, A quarter of a mile further on, in Folly Quarry, an oliv in e­ basalt dyke pierces the red conglomerate . Th e dyke shows vesicula r bands parallel t o a t achylytic edge . Th e Director stat ed that the rock differed from the olivine-dolcrites of Wast ­ water , which were post -Triassic, and was probably Carbo niferous; his slide showed a rock composed of lab radorit e lath s about half a millimetre long wit h much small augi te and magnet ite and fresh olivine phen ocrysts. In reply t o Professor Oha shi , who observed that in J ap an such thick dykes were 11 0t so 'fine­ grained throughout , he said that his specimen was taken ab out four feet from the edge and that probably the middle was mu ch coarser. On exa mination considerable var iation was evident. The remarkabl e semi-ci rcular gorge at H olghyll was next visited . H ere nearly horizontal Carboniferous Limest one lies along the top , while below is a great sect ion of red sandst one a nd conglomerate, dipping at IS°. Th e mat erial is finer-gra ined t han at Little Mell Fell, the boulders are separa te d by sa nd, stru ng out like bead s or irregularl y disposed like curr ants in a bun. The Director thought this stru ctur e diagn ostic of con­ tinental conditi ons, but some present regarded it as consistent with beach deposition. The pebbles are largely igneous, many being granites or quartz-porphyries, among which Professor Fearnsides found a boulder of garnctiferous granite-porphyry. Taking train from Penruddock to Troutbeck, most of the party went towards Eycott Hill , crossing Lofshaw Hill , a whale­ backed drumlin with many boulders of Threlkeld granite -por­ phyry, swept up-hill by the Helvellyn icc. Below Eycott Hill, a °Gf ol. 1If~1. 1900, p . 564. 128 J. F. x. GREEN, bed , about ten feet thick , of material resembling slightly h01 n­ fclsed Skiddaw Slate, lies between t wo lavas. The Director commente d on this and on the abs ence of evidence for the fault inserted on existi ng maps between the vo lcanics and the Skidda w Slate. Then some members went up the hill t o collect specimens of the bytownite-bearing lava, while others remained t o watch a demonst ration of panning by )1r. Kitson. The concentrates taken at the base of th e bytownite-lava from a little gill rising in the lavas contained some red garnet, derived probabl y from the E ycott rocks. A L" Gt.:ST IITH. L O:-lG SLED DALE A~ D SADGHYLL. THE party motored from Penrith t o Mardale, an d set ant immediately for th e Gat esgarth Pass, the first halt being mad e on the other side at the Wrengill quarries. Here the Dir ect or demonstrated the cha racte rs of the Middle Tuffs and explained the manner in which at this point the Wrengill Andesit es carne in from the west. "

between the old filled-up lake of Mardale, nearly a mile long. and Haweswater. The damming of the latter in connection with the Manchester water-supply will drown Mardale village and lengthen the lake by a mile and a half. The water will be drawn off by a tunnel under . In the evening the Director exhibited, in illustration of his ascription of the "bird's-eyes" to concretionary action, some large weathered concretions in tuff from Easdale Tarn, where they are found over two feet in diameter. ACGUST 12TH. WATCH HILL, SALE FELL AXD BASSEKTHWAITE. ON leaving Embleton Station the party went up Lambfoot Rake to Dodd Crag, where polygenetic grit is interbedded with black and g~een shales ncar the level where the grits (Watch Hill Beds) lie on the Skiddaw Slate, not far from the western end of an eleven-mile series of outliers, the eastern end of which had been seen at Silver Gill. Here too it seemed that there must be either an unconformity or a thrust. Some time was spent fruit­ lessly searching for fossils, nothing but worm-tracks and burrows being found. Proceeding to the top of Watch Hill, the Director pointed out the old pre-glacial course of the River Derwent to the south, blocked by mounds of drift with intervening alluvium marking old tarns; a modern drift watershed at Netherscales ; the new course of the Derwent to the north; Bassenthwaite Lake partly held up by a drift-bar; the fells to the north com­ posed of gently-dipping Carboniferous resting on Borrowdale volcanics ncar their junction with the Skiddaw Slate, through which pre-Carboniferous valleys had been cut and filled with red conglomerate and sandstone; the evidence for low sheet-dip; and the position of the eappings of polygenetic grit on the neighbouring ridges. He described the materials of the grit and their variation from west to cast, corresponding to the variation of the pre-Bala rocks now exposed, and inferred that there was an unconformity. A quarry ncar the top of the hill, opened in a columnar, highly altered felsite resting on the grits, was next visited. This was compared with the Stockdale rhyolite, which rests on the basal Bala sandstone for a large part of its course. Passing by some brickpits in the alluvium of a former tarn, the next section, at Fellcnd Quarrif's, was in biotite-dolerite. The Director said that this was one of a series of exposures noted for five (possibly eight) miles on the Survey map, which clearly be­ longed to a continuous intrusion, probably a sill marking a definite horizon in the Skiddaw Slates; but it appeared to be the practice in the old maps to colour actual exposures only of such intrusions. intervening drift being coloured as country-rock. The same method had been adopted in the case of the olivine-basalt dyke of Folly.* ·Page 127. 13° J. F. x. GREE~, The dolerite shows shear-lines attributed to the Devonian folding, the igneous rock breaking while the soft slates crumpled. After lunch the party crossed moraine-mounds (in the pre­ glacial Derwent valley) to 'the south of Sale Fell. Halfway up the fell, Professor Fearnsidcs found a new fossiliferous locality with Tetragraptus quadratus and other graptolites. At the top speci­ mens were collected of the well-known minette; boulders of this rock are found for miles both north and south of the exposure, so that it seems that the Scottish and Lake District ice-sheets alternately drove over the summit. Next a descent was made to exposures of polygenctic grit on the northern slope of the fell, which the Director regarded as keels of overturned synclines. Most of the party took an opportunity before tea of visiting the .ancient British fortifications on Castle How. After tea many walked to Dubwath Bridge to sec a channel, cut in drift, draining an old tarn, over a mile long, into Bassenthwaitc Lake. The freshness of the sides of the channel which, though cut in incoherent moraine-stuff, retained their original shape, is remarkable.

Al;GUST 13TH. TIlE TU:\"GSTEN MINE AXD SKIDDAW AUREOLE. Ox leaving the motors at Mosedale Bridge the party, numbering 79, walked along the Caldew valley to Swineside,: where an unclcavcd hornfels of the Skiddaw aureole had been cut. In this exposure the ottrelite-like mineral described by Mr. Rastall,* is larger than known elsewhere, being often a quarter of a millimetre long. In the River Caldew, 200 yards before reaching the junction with Grainsgill Beck, are large exposures of intensely contorted, but uncleaved, garnet-cordierite-horn­ fcls (without the ?ottrc1ite) the folds pitching at all angles, but preserving a general parallelism to the boundary-fault between the sedimentarios and the Carrick Fell intrusions. At the Tungsten Mine quantities of wolfram, scheclite, arseno­ pyrite, and green apatite were collected with smaller amounts of other minerals. The Director pointed out that the veins had an alignment believed to be Hercynian, and had been mapped by Ward as along faults shifting the neighbouring greisen, the Mosedale fault (probably Devonian), and the cast-west faults of the Drygills. On the other hand some considered these veins to be related to the grcisen, which bore much mispickel. This interpretation would make the greisen post-movement. He thought, however, that evidence to be seen later in the day proved beyond doubt the pre-cleavage age of the Skiddaw intrusion, of which the greisen was held to be part. The question was one of mportance in connection with the origin of ore-deposits. Turning back to go up the Caldew valley, the greisen was -Qua 1t. ]OIITIt. Geol, Soc., vol. lxvi, 19IOJ p. 126. PROe. GEOL. Assoc., VOL. XXXII. PLATE 5.

P"o/~1 J. lit. Rhoc!ts. A -FOLDED HOR:

PIi{J!o J. J. Hinllcv, B.-]OIXTED FELSITE XEAR SC)IMIT OF \\'ATClI HILL, T" face t. 130. LONG EXCURSlO~ TO THE LAKE DISTRICT. 131

seen in the beck, in contact with hornfels, and abundant evidence found of the presence of arscnatcs. Opposite the mouth of Blackhazel Beck, by the junction in the Ri ver Caldew of the centralgraniteand garnet-cordicrite-rock, the Director gave a general description of the metamorphism, exhibiting Mr. Rastall's map,* and contrasted it with that around masses intruded at a higher level, such as the Eskdale granite. He attributed the difference to retention of water and other fluxes at greater depth, as evidenced by the failure of the Skiddaw granite to drive off carbon, so far as microscopic exa­ mination showed; and considered that this type of contact­ alteration afforded a transition to regional metamorphism. Mr. Barrow's regional zones in the Highlands followed the order biotite, garnet, staurolite, kyanite, sillimanite, the succession of the last two suggesting thermal, rather than dynamic altera­ tion, since sillimanite had a lower density than kyanite. In the Skiddaw aureole chiastolite (or andalusite) appeared throughout, but biotite, garnet and staurolite zones were found as in the Highlands. Kyanite and sillimanite were not reached. Twenty-three members got across the River Caldew and visited the junction of granite and contact-rock in Blackhazcl Beck. A rude cleavage, apparently coincident with bedding, was seen close to the granite, but 400 yards farther up a good cleavage, cutting folded bedding, was found. The rock is a coarse garnet­ cordieritc-homfcls which might almost be called a gneiss. It was stated that the cleavage could be followed up along the beck, which cut a section a mile long, and over a col, into normal Skid­ daw Slate; the breadth of the aureole here being a mile and a half. At the head of the Glenderaterra valley a fine view was ob­ tained down the great gap to Dunmail . A few left here, under the guidance of :vIr. ]. W. Rhodes, to visit the granite at Sinen Gill, where contortions arc seen in the hornfels. The majority followed the track to Roughten Gill, where they saw a fully recrystallised rock outside the .garnet-zone in a well-cleaved condition, containing torn-out chiastolite pseudomorphs. The high-level eastern track was then taken for a third of a mile to an exposure in the outer part of the aureole where the rock was still strongly cleaved, but showed a great development of perfect chiastolites, often over an inch long. The Director gave reasons for regarding the cleavage as later than the formation of the chiastolites, which had been protected by the flowage of soft, almost unaltered, shale round them. AUGUST 14TH. SEATHWAITE, GILLERcmIB AND THE STYHEAD PASS. THE conveyances stopped at Lodore, which was at its best, owing to the continued wet. The Director pointed out the posi- -Quart [ourn, Geol, Soc., vol. lxvi., 1910, pl. xiv, I3 2 J. F. N. GREEN, tion of the junction between andesite and Skiddaw Slate under­ lying, which could be followed across the bed of the cataract and along its southern wall. He considered that there was no trace of shattering or faulting, but that the gorge was due to erosion along the soft slate, the overlying hard andesite falling down in the great joint-blocks that built the cascade. The brakes then went on to Seathwaite Farm,whence the party walked up to the old plumbago mines, where numerous specimens were collected. The Director gave an account of the history and uses of the mineral. Climbing up to the lip of Gillercomb, a halt was made by Sourmilk Gill at the junction of a great breccia and overlying bedded tuffs. So far as mist allowed, the Director pointed out the notable freshness of the combe, the hanging valley and the moraine-mounds, though in a district of heavy annual rainfall ; and, recalling other instances which had been noted, suggested that the final glaciation and the glacial deposits of the district could hardly be older than the period, shown by De Geer to be gooo years ago, when the Scandinavian icc-sheet was withdrawing from Stockholm; corresponding probably to the transition between palreolithic and neolithic. There was a vast difference compared with the erosion which had taken place since the deposition of the southern boulder-clays, which must be far older. The broad deltas and deep infillings of the Lake District appeared to be composed of the incoherent glacial drift cleaned out of their old courses by the streams, which had done very little rock-cut­ ting; and most of this cleaning-out must have been done in a short period, as the deltas had made only negligible advances in historical times, witness the Roman fort at Ambleside. He then pointed to the sequence of Wrengill Andesites, Harrath Tuffs, Upper Andesites (columnar) and Rhyolites, seen in the slopes of Base Brown. The extraordinary breccia upon which they were standing was the most remarkable development of which he was aware, presenting some quite special features. He believed it to be the highest lava-crust of the Wrengill Andesites. Professor Fearnsides drew attention to a comparatively smooth surface, covering perhaps fifteen square yards, between the coarse breccia and the neatly bedded tuffs. This the Director ascribed to the flow of a viscous fluid filled with blocks of the same density, considering that an agglomerate should have a rugged surface. Some of the party, however, thought that lenticles of bedded tuff within the breccia pointed to an agglo­ meratic origin, but the Director promised to illustrate the method of their formation at Woof Crag on Monday.* A rough walk was then taken to the head of the almost circular combe, passing marshy remains of a tarn and exposures of a small laccolith of dolerite, up through a subsidiary combe, over the col of Blackmoor Pols. Climbing down to the track up the Styhead Pass, large exposures of both normal and streaky rhyolite were crossed. • Page , '36. LOXG EXCURSION TO THE LAKE DISTRICT. I33

Some members now took the road down to Seathwaite, the remainder turning towards Styhead Tarn. A little below the tarn, just at the junction of the Rhyolites and the Upper Ande­ sites repeated south of the track, nodular rhyolite, not previously recorded, was found. The Director commented on the interest of this discovery, as being on the same stratigraphical horizon as the widely spread nodular rhyolite of the Haweswater district. namely, at the base of the Rhyolites. The dry delta* blocking Styhead Tarn was well seen from above. The position of the shatter-band dividing and Green Gable was noted and it was observed that the stained rock, as could be seen in the debris, was closely jointed, but not brecciated. The Director understood that the term" shatter-band " was not in­ tended to imply brecciation in the usual sense. At the top of the pass a splendid view was obtained of the precipitous mountains and downWasdale to the sea. The Director described the composition and structure of the mountains surrounding Wast­ water and ascribed their steepness to the general absence of tuffs. On the way down, garnets and numerous varieties of " streaky" rhyolite were collected, a gradation being shown from flow-breccias containing stumpy lenticles, only slightly pulled out, to delicately banded rocks. Taylor Gill Force and other falls from hanging valleys were seen.

AUGUST IS-rH. \VATE:-;DLATIl A:-;O QCAYFOOT. MOTOR-BOATS were taken up Derwentwatcr, a few members first examining the junction of the Castle Head dolerite] and Skid­

AuGUST r6TH.

HAWESWATER AXD SWIXDALE.

THE motors from Penrith made their first stop at Measand Beck, where ascent was made to the Forces, at the lip of a hanging valley. The gorge is cut through an infold of streaky rhyolite and the top of a laccolith of quartz-dolerite. Naddle Forest, last remains of the primseval wood that covered the district till

·~Iarr, Geology of the Lake District, P. '95. tAncient Volcanoes 01Great Britain, vol. L, page 23I. LONG EXCCRSIO~ TO THE LAKE DISTRICT. 135

media-val times, was seen across Haweswater and attention was drawn to the delta of Measand Beck, about 25 acres in area and at least 100 feet thick, which had nearly severed the lake. The rock-gorge could not have contributed one-thousandth of the material. Half the party then walked a mile along the margin of the infilled tarn known as Fordingdale Bottom, to Fordingdale Forces, two small waterfalls over nodular rhyolites about forty yards apart. This nodular rock had been mapped by the Survey on Kidsty Pike, converging from points a quarter of a mile apart; E. E. Walker in Ig01 discovered some new exposures during his investigation of the" streaky" rocks and noted duplication in Fordingdale and Randale Beck. 'When the Director attacked the district, he had already been convinced that the :" streaky" rocks were merely the ordinary Lake district soda-rhyolites with some secondary infiltration, and he accordingly set to work at the line between rhyolite and andesite. He soon found that the nodular lava only occurred at the boundary,and had identified it frequently. Probably it could be found at the base of the rhyolites everywhere in the Haweswater-Sadghyll district, but it was not easy to recognise off-hand when the nodules were small. The discovery on the same horizon on Saturday at Sty­ head,* seventeen miles away, was of considerable interest, and the flow should be searched for in intermediate infolds, which were numerous. It was curious that the basal flow next to the Upper Andesites should have a silica percentage ncar 80, while the higher flows were usually under 70, so far as analyses were available. t The structure was described as an overturned syncline, nearly cut in two by Fordingdale Beck, and andesite was identified both above and below the waterfalls. While the nodules are marc resistant to ordinary weathering than the rest of the rock, the opposite is the case under or ncar water. Returning to the motors, all went on to Mardale, whence, after lunch, fifty went up the Rake, crossing closely folded-up tuffs and lavas, towards the guidepost for Swindale. The Director at first missed the direction for Woof Crag, and some time was spent searching for it, during which the party became separated, so that only twelve saw this remarkable exposure.] which shows a small dyke cutting strongly fluidal flow-brecciated hypersthene-andesite with garnets. The material of the dyke appears identical with that of the breccia (which shows little or no trace of brecciation on a freshly broken surface) and the breccia itself behaves intrusively to the ropy portions of the crust. The face of the section was not hammered, but specimens were °Page '33. tMost of the rhyolites seem to range from 68 to 73. A specimen south of Haweswater, prob­ ably the nodular rhyolite, has a percentage of 82.25. The andesite of Fordingdale has 56.95. See Harker, Naturalist, 189<),pp. 56, ~7. :Proc. Geol, Assoc., xxvL , 1915, pI. 17. 136 J. F. N. GREEN, collected from the back and sides. The Director pointed out that, when a lava-crust broke on a large scale and sank into the underlying melt, as had happened here, the fluid lava rising through the cracks would flow over the surface, overwhelming bedded material which, as a result of blow holes, etc., would always be forming on the top of the crust. This would explain at least part of the peculiarities of the exceptional form of breccia at Gillercomb; and no doubt, as in the case of little para­ sitic vents on subaerial lavas, action at one point might be con­ tinued at intervals for some time. Descending into Swindale, the Director's party visited the tiny church and school, and then kept along the north side of the valley to see infolds of the Flagdaw type of Mottled Tuff in Swin­ dale Beck and at Rawhead. On the way the fault ncar Swindalc Foot, and its effect on the topography, were pointed out. The junction of the tuff and Skiddaw Slate in the quarry between Rawhead and Toathmain was much obscured, but was dug out. Some others went along the south side to Tailbert and found the conformable junction of Mottled Tuff and Skiddaw Slate. In the evening Mr. and Mrs. Green and Mr. Postlethwaite were the guests of the Association, and the usual votes of thanks, which included Mr. J. W. Rhodes as Assistant Director and Miss Bauer, who acted as Excursion Secretary, were accorded. Mr. Postlethwaite exhibited a number of remarkable local speci­ mens.

ACGL'ST 17TH.

ST. JOlIN'S AND THRELKELD. O~ the way towards St. john's-in-the-Valc a section of the junc­ tion of andesite and Skiddaw Slate was seen in a little gill near Causeway Foot. This junction was mentioned by Nicholson- in 1871, and had recently been rediscovered by Mr. Postlethwaite. After the various horizons in the opposite side of the Naddle Valley had been pointed out, speciil attention being drawn to a feature made by Skiddaw Slate between granite-porphyry and andesites, the party followed footpaths to the neighbourhood of Sikes Farm, where they saw a flow-breccia with a conglomeratic appearance in places. The Director ascribed the rounding of the fragments to fusion and stated that in his experience gocd flow-conglomerates only occurred in the more basic lavas. He contrasted this rock with a fault-breccia in a neighbouring quarry. The St. John's granite-porphyry was then crossed to an exposure near Skelthwaite Crag of hornfelsed and rudely cleaved Skiddaw Slate, regarded as part of the roof of a sill. Descending to the side of St. John's Vale a line of quarries in the ·Qua,t. ]ourn. Geol, Soc., vol, xxvl., p. 603 LONG EXCURSION TO THE LAKE DISTRICT. 137

Threlkeld granite-porphyry was seen, and the Director pointed out successive" platforms" of Skiddaw Slate, porphyry, folded­ up Skiddaws and andesite, and finally andesites. As the dips in the Skiddaw Slate above and below the intrusion were high, the apparent low general dip must be a sheet-dip. The valley was then crossed to some powerful springs at Wanthwaite, thrown out at the junction of the granite-porphyry, which was highly jointed and therefore capable of holding water, and the more impervious Skiddaws. The President made some interesting remarks on springs generally and their importance in mapping. As was shrouded in dense cloud it was decided not to go up to the junctions there, but to study the porphyry in the quarries. The Director considered that the slickensided master-joints were controlled by the Devonian folding and in­ dicated adjustment of hard porphyry by fracture between a roof and floor of crumpling Skiddaw Slate. An excellent illustration of this was found by Mr. J. Spencer, who discovered the floor of the sill exposed on both sides of a tramway cutting on Birkett Bank, showing the junction repeatedly faulted a foot or two along the joints. Meanwhile numerous xenoliths, mostly more or less altered sediment, had been seen and Professor Schwarz had found some large garnets in the porphyry. The next stop was at the remains of an old British village above Threlkeld Quarry. Professor Schwarz commented on the resemblance to the Inyanga ruins in Rhodesia. Excavations at the similar, but much larger, ruins at Barnscar show that the people buried their dead in urns after incineration. The village is generally regarded as Romano-British. It was presumably situated in a clearing in dense forest and, like others, was placed well above the bottom of the valley, probably then a swamp, largely held up by beaver-dams. At this point Mr. Barrow, of the Threlkeld Granite Co., welcomed the party and led them to a safe spot in the quarry to see a large blast, which brought down several hundred tons of rock. The east end of the quarry cuts the slate floor of the sill for a considerable distance; the west end is bounded by a fault with a thick breccia arid splendid slickensiding. Many specimens of interest were collected, among others tourmaline and a banded siliceous xenolith, found by Mr. Kitson, containing malachite and manganese. The party were then taken over the whole of the processes, beginning with blasting and sett-making, through the machinery for breaking and sifting the stone, making tar-macadam and art-tiling, and finally to the railway-siding, where the various products were loaded. All were impressed by the organisation and efficiency of the works, which produced from eighty to a hundred thousand tons of stone a year. At the offices Mr. Barrow exhibited a re­ markable deposit of calcite in successive spirals on a joint-plane of porphyry, which evoked much comment. 138 L O~ GE X C UR SI O~ TOTHE LAKE DI STRICT.

At the instance of th e President, a heart y vote of thanks was give n to the Company and to Mr. Barrow for th eir courtesy an d trouble. Afte r return t o Keswick a visit was paid to the Museum. Specimens exhibited included fine examples of quartz, kam pylitc, linaritc, brochantite, alsto nite, ph arrnacosideritc, garnet, graphite and othe r local min erals ; of Stellascolites, Didymograptus patulus and othe r fossils; the un ique Cybele ovata ; unpolish ed celt s ; an d a collection of polish ed specimens of the chief intrusive rocks of the Lak e District. In the museum itself beautiful geologica l relief-maps, prepa red under the direct ion of J. C. Ward, were mu ch admired ; and th e Direct or gave some acco unt of the large and carefully labelled series of rocks an d maps presented by that worker. [NoTE.-While the above was in the Press, I received a com­ munication from Mr. C. C. Duncan, F.I.C., F.C.S., who had kindly undertaken to test for carbon a specimen of cordierite-hornfels from the sluice in Grainsgill, which I had described as graphitic. He writes as follows :- " The rock was ground to a fine powder and a combustion made in a quartz tube in an atmosphere of oxyge n free from CO2 and S02' A distinct quan tity of S02 gas was given off. " The alkali into which the gas was passed origina lly con­ t ained no Carbonate and afte r th e experiment I was un able to detect the pr esence of a Carbonate. The rock therefore did not contain any free Carbon . .. Another portion of the finely divided rock was treat ed with HCI and warmed , when an obvious odo ur of H 2S was d etect ed . A readil y decomposed Sulphide was pr esent , probably FeS and not FeS 2> as the latter is insolu ble in HCI. .\ sulphur determination was made and, calculated as FeS, gave 5.7 per cent. of FeS in the origin al rock. " The explanation which I have suggested for the decolorisa­ tion of Skiddaw Slate by certain intrusions is therefore in­ correct, at all events so far as the nature of the min eral in question is concerned.-]. F. N . G., I-3-21.]