H. HICKS ON AND CLASSIFICATION. 105

The Arenig Group, which comes in next in the Table, is divided into an Upper and a Lower series, both characterised by a distinct assemblage of fossils, The Lower series occurs chiefly in the neighbourhood of St. David's, and is of about 1,000 feet in thick­ ness. The fossils consist of numerous graptolites, especially dendroid forms, and of the genera Ogygia, Trinucleue, and .k:glina. All the forms are thoroughly Silurian in character, and the series marks a definite line for the base of the Silurian groups. The Upper series comprise the well known Skiddaw Slates. Upon the Arenig comes the Llandeilo Group, the lowest rocks recognised by Sir R. Murchison in the typical Llandeilo district. This group in the Table is divided also into an Upper and Lower series, marked out by distinct faunas. The Bala or Caradoc Group now comes in with its exceedingly rich fauna, and it forms in the Table the upper member of our Lower Silurian, and also of Professor Sedgwick's Upper Cambrian. Sir R. Murchison added to the Lower Silurian the Lower Llandovery rocks, but Sir Charles Lyell in his" Student's Manual of Geology," 1871, preferred "to regard them as the base of the Upper Silurian, to which group they are linked by more than twice as many as to the Lower Silurian." The evidence of Professor Hall and others, in America, tends to prove, however, that ultimately it will be necessary to make a Middle Silurian division, and though the group is scarcely important enough, as hitherto known in this country, to warrant such a division, yet should a spot be found where the present unconformity is filled up, a series may be discovered, like that in the American continent, sufficiently large to enable it to be done. The higher groups, Wenlock and Ludlow, which complete the Table, are each capable of being divided into at least two groups, with a considerable thickness of strata and well defined faunas.

2. ON THE SILURIAN ROCKS OF THE ENGLISH LAKE DISTRICT.

By H. ALLEYNE NICHOLSON, Esq., M.D., D.Sc., M.A., F.R.S.E., Professor of Natural History and Botany in University College, Toronto. Considering the extent to which the Silurian series of the Eng­ lish Lake District has been studied, it is somewhat remarkable that there should still be considerable difference of opinion as to the 106 PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. ages of its various members, their correlation with the deposits of other areas, and, in some cases, even their actual succession. In the following communication I propose briefly discussing this sub­ ject, and in so doing I shall speak of the following groups of strata :-

1. The Skiddaw Slates. 2. The Borrowdale Series, or Green Slates and Porphyries. 3. The Ooniston Limestone and Associated Shales. 4. The Graptolitic Mudstones. 5. The Ooniston Flags. 6. The Coniston Grits. 7. The Kendal Rocks.

I. THE SKIDDAW SLATES. The lowest sedimentary rocks of the Lake District are unques­ tionably those to which Professor Sedgwick applied the name of " Skiddaw Slates." This group comprises a great series of dark cleaved shales, with intercalated flaggy beds, which reach a total thickness of probably not less than about 7,000 feet. The upper beds of the series are generally readily distinguished from the lower, by being darker in colour, by being of a more fissile or shaly nature, and by being usually very imperfectly, or not at all, cleaved. As yet, however, no accurate line has been drawn between the upper and lower portions of the series, and some of the most characteristic fossils are common to both. As to the relations of the Skiddaw Slates to the rocks which succeed them (the Borrowdale series), ithas been generally believed that the highest beds of the Skiddaw series were conformably over­ laid by the base of the Green Slates and Porphyries, and this opinion is still held by high authorities. I have endeavoured, however, to show (Geol. Mag., vol. vi., March, 1869) that this is not the case, and that the Skiddaw Slates are unconformably sur­ mounted by the basement-beds of the Green Slate series. To this opinion I still adhere; but having no fresh evidence to bring for­ ward in support of my views, I need not press this point at present. As regards the palreontological relations of the Skiddaw Slates, it has long been known that they contain a very rich and varied graptolitic fauna, comprising many peculiar forms. No less than nine genera and thirty-two species of graptolites have been de- PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. 107 tected in the Skiddaw Slates; and five genera (viz., Dichograpsus, Tetraqrapsus, Loqanoqrapsus, Phyllograpsus, and Triqonoqrapeus ), are exclusively confined to this horizon. All these genera, how­ ever, and a large number of the species, occur in the so-called "Quebec Group" of Canada; and there can, therefore, be no reasonable doubt as to the contemporaneity of the SkidJaw and Quebec groups. The most important fossils yielded by the Skid­ claw Slates, besides graptolites, are, Lingula brevis, the peculiar phyllopod Caryocaris Wriqhtii, and the trilobites, lEglina bino­ dosa, ./Eglina caliginosa, Agnostus Morei, Phacops Nicholeoni, and Trinucleus Gibbsii. In applying the stratigraphical and paleeontological elements at our disposal to the solution of the question of the age of the Skid­ daw Slates, we find ourselves beset with unusual difficulties. The physical evidence only tells us with certainty that the Skiddaw Slates underlie strata which at the utmost cannot be older than the Llandeilo Flags of Wales. If the Skiddaw Slates were conform­ able to these, there would be the probability that the Skiddaw series is not older than the Arenig rocks of Wales, as is believed by Professor Harkness. Even in this case, however, the Skiddaw Slates can hardly be said to be the equivalent of the Arenig group, as the latter contains none of the peculiar graptolites of the for­ mer. If, on the other hand, the Borrowdale series (as I believe), rests unconformably upon the Skiddaw series, there is a high pro­ bability that the latter is older than the Arenig, and that it cor­ responds to part of the Upper Oamlrians. The paleeontological evidence, though more satisfactory than the physical, still leaves much to be desired. The great majority of the Skiddaw grapto­ lites occur in no other British formation, aud do not, therefore, supply any element of comparison so far as Britain is concerned. No stress, also, Can be laid upon the occurrence of some four or five of the Skiddaw graptolites in the Arenig and Llandeilo de­ posits of Wales. The phyllopod Caryocaris Wrightii, so abundant throughout the whole Skiddaw series, is also peculiar to this hori­ zon, and affords, therefore, no means of comparison. The tri­ lobites, on the contrary, belong to the Silurian genera, or at least to genera all of which are represented in the Silurian series. The Phacops, in particular, has not yet been detected in rocks undoubtedly older than the Silurian. There are no "primordial" trilobites j and the evidence, therefore, to be drawn from these 108 PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. crustaceans would lead us to believe that the Skiddaw Slates are referable to the Lower Silurian series. On one point only do the fossils of the Skiddaw series speak with certainty, and that is as to the equivalency of the British formation with the Quebec Group of Canada. All the pecnliar genera of graptolites in the Skiddaw Slates occur also in the Quebec Group, and in Canada, as in Britain, they do not occur in any younger formation, with rare exceptions. At least half of the Skiddaw species are also identical with Canadian forms.· We may, therefore, safely conclude that the Skiddaw and Quebec groups are " contemporaneous" deposits, in the geological sense of this term. It follows from this that the age of the Skiddaw Slates might be fixed without difficulty, if only the age of the Quebec Group were known with certainty. Unfortunately, however, the precise age of the Quebec rocks is still a matter of opinion, for they contain a mixture of ,. primordial ,. fossils with genuine Silurian types, and their stratigraphical position is also somewhat uncertain. As regards the first of these points, we meet in the Quebec Group with the Silurian genera Asaphus, Cheirurus, Illamus, and Lichas, mingled with" primordial" trilobites of the genera Dikelocephalus, M enocephalus, Bathpurue, and Bathsiurellue. The brachiopods, gasteropods, and cephalopods are, on the other hand, referable to types which are characteristic of the Lower . The Quebec Group has generally been regarded as belonging to the same formation as the Calciferous Sand-rock of the State of New York, which immediately overlies the Potsdam Sandstone, and the age of which appears to' be indubitably Upper Cambrian. In Newfoundland, however, the Quebec Group (" Levis formation") has been described as being separated from the" Calciferous" byover two thousand feet of other strata. If there be no disturbance of the strata this would show that the Quebec Group is considerably younger than the Calciferous; but it is not impossible that the phenomena admit of some other explanation.

II. BORROWDALE SERIES. Overlying the Skiddaw Slates comes the great series of rocks termed by Professor Sedgwick the" Green Slates and Porphyries," for which the name of " Borrowdale Rocks" has been proposed by Professor Harkness and myself. These consist essentially of a vast succession of bedded traps and porphyries, with stratified felspathic PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. 109 ashes, breccias, and amygdaloids. The great mass of the series is of igneous origin, but I am unable to agree with Professor Ramsay in believing that the rocks of this series are sub-aerial. It is with great diffidence that I differ from so distinguished an authority, but I am decidedly of opinion that the traps of this series were poured out beueath the sea, and that the ashes have been subjected (in most instances at any rate) to the sorting action of water. Near the summit of the Borrowdale series there is found a thin group of beds, sometimes of an ashy, sometimes of a shaly nature, which have been shown to contain in places a number of ill-pre­ served fossils. These beds, beyond all question, underlie the Coniston Limestone, from which they are separated by a mass of trap, and they are, therefore, truly a portion of the series of the Green Slates and Porphyries. Amongst the fossils which they contain may be mentioned Petraia subdaplicata, Calymene Blumen­ bachii, Orthis vespertilio, Orthis flabellulum, and Strophomena tenui­ striata. These fossils leave little doubt but that the upper portion at any rate, if not the whole, of the Borrowdale series is referable to the Caradoc or Bala period. Beyond the limits of the Lake District proper, a remarkable series of fossiliferous beds has been described by Professor Harkness as occurring beneath the Penine Chain, under the name of the "Dufton Shales." These beds are replete with Bala fossils, and their age is thus rendered indisputable. Their stratigraphical position, however, is not so certain. By Professor Harkness they are regarded as belonging to the series of the Green Slates and Porphyries, as underlying the Coniston Limestone, and as corres­ ponding to the thin fossiliferous band found in the Lake District, near the summit of the Borrowdale series. After a careful and repeated examination of the district in question, I have been led to entirely adopt the views of Professor Harkness upon this sub­ ject ; but I believe that Mr. Hughes is of the opinion that these beds are not truly referable to the Green Slate series. No such doubt, however, can, in my opinion, be entertained as to the posi­ tion of certain other fossiliferous beds which were described by myself under the name of " Swindale Shales." These beds occur in the same Silurian area beneath the Penine Chain, but they are inferior in position to the Dufton Shales, and I feel no hesitation in considering them as a portion of the Green Slate series. They occur in the course of Swindale Beck, near the village of Knock, 110 PROF. R. A. KICHOLSON ON THE LAKE DISTRICT. in Westmoreland, and they consist of brownish ashy beds, with black flaggy shales, and green and purple slates. They contain numerous fossils, which belong to common Caradoc types, and which are in most instances identical with the organic remains of the" Duft on Shal es." Apart, therefore, from the evidence afforded by the thin fossiliferous band in the Green Slates of the Lake Dis­ tri ct, I think we have satisfactory grounds for believing that th e enti re Borrowdale series, or g roup of the Green Slates and Por­ phyri es, is of th e age of the Caradoc beds of W ales.

III. C ONI STON LIME STONE. Overlying the Borrowdale Series with perfect conformity, we have the formation describ ed by Prof. Sedgwick under th e name of the "Coniston Limestone." This consists, in the Lake District proper, of several bands of limestone separated by intercalated hard gray or bluish cleaved shales. It is unnece ssary to consider the fossils of the Coniston Limestone, as it is universally conceded th at this formation is th e equivalent of th e Bala Lim estone of W ales. In the neighb ourhood of Sedbergh, however, Mr. Hugh es has shown that th e Coniston Limestone passes upwards into a con­ siderable thickness of shaly beds, which he terms "'l'rinucleus Shales" and" Strophomena Shales," from th e occurrence in them of Trinucleus COllcentdcus and a lar ge species of S troplunnena. I had the pleasure of examining these beds under the guidance of Mr. Hugh es, but I am disposed to regard them as nothing more th an a great development of some of the shale-beds which are uni­ versally present in th e Coniston Limestone in the Lake Distri ct. It is quite certain that in the Lake District proper the bands of limestone extend to close upon th e summit of th e ser ies ; and the "Strophomena and Trinu cleus Shales" of Mr. Hugh es, if not altogeth er absent, are at most repr esented by no more th an a few feet of fossiliferous shales. W est of Coni ston Lake, however, the series assumes more th e character "IV hich it exhibits in th e Sedbergh district; and in the extreme west, in the neighb ourhood of MilIom, there is a considerable mass of shale overlyin g th e high est bed of actual limestone. It docs not appear to me, however, that any satisfactory separati on, physical or palreontological, can be made between the limestone and th ese overlying shales, and I should be disposed to gr oup both under the name of " Coniston Lime­ stone." PROF. H. A. NI CH OLSON ON THE LAKE DISTRICT. 111

IV. GRAPTOLITIC MUDSTONES.

Immediately above th e Ooniston Limestone, and as far as the pr esent evidence goes, surmounting it with entire conformity, comes a small but remarkable g roup of beds which have been descri bed by P rofessor H arkness and myself under the name of the" Gr ap­ toliti c Mudstones." These beds consist of a series of black and grey shales and mud stones charged with the remains of grapto­ lites. As no graptolite has hitherto been discovered in the richly fossiliferous shales associated with the Coniston Lim estone (though their na ture is such that graptolites might well be expected to occu r in the m), th e contrast between these and th e immediately overlying and contiguous mudstones is of an exceedingly striking nature. The graptolites of the Mudstones, though in many cases peculi ar to this horizon, are in the main wonderfully similar to th ose of the Upper Lland eilo shales of Dumfriesshire, including species of the ge nera D iploqrapsus, Climacoqrapsus, and Iiastrites, Besides graptolites, th ey hav e only yielded Endoceras proteiforme of the Lower Silurian rocks of North A merica ; th e Bala fossils Sp ha ronites punctatus and Orthis calligramma (1), and some un­ descri bed crustaceans and orthocera ta, As to the age of th ese beds th ere is still some difference of opinion. For my own part, I still adhere to the opinion originally expressed by Professor Harkness and myself, that the Graptolitic Mudstones are of un­ equivocal Lower Silu rian age. I consider that this is placed beyond all question by th e character of the graptolites. At the same tim e I am pr epared to abandon the view which I formerly h eld, th at the Graptolitic Mudstones form a portio n of th e series of the Oonisto n F lags. On the contrary, the researches of Mr. Hu gh es seem to have conclusively shown that the Ooniston Flags are essent ially distinct from the Graptolitic Mudstones, th ough I am not aware th at in any instance the stratig raphical relations be­ tween the two have as yet been satisfactorily determined. I need only add that whilst t he Graptolitic Mudstones rest in the Lake District upon the Ooniston Limestone itself, th ey repose in the Sedbergh District upon the " Trinucleus and Strophomena Shales " of Mr. Hu gh es. Sup eriorly, the Graptolitic Mudstones appeal' to pass upwards with complet e conformity into th e ordinary Oonisto n Flags, and I have never been able to detect any sign of a discordance between the two. Still, the actual junction bet ween 112 PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. these formations has not yet, so far as I am aware, been observed; and there is thus some room for doubt as to the relations whicb subsist between the two. There is, also, undoubtedly a marked change in the fauna, which is especially noticeable as regards the graptolites. Thus, the Graptolitic Mudstones contain numerous species of Diplograpsus, along with examples of the genera Climacograpsus and Rastrites ; and the great majority of the specific forms (when not peculiar to this horizon) are identical with well-known forms from the Upper Llandeilo shales of Dumfries­ shire. On the other hand, the Ooniston Flags proper have yielded no specimens referable to the above-mentioned genera, and contain only examples of the two genera Retiolites and Graptolites, both of which pass np to the very summit of the Silurian Series.

V. THE OONISTON FLAGS.

The Graptolitic Mudstones are succeeded upwards, whether con­ formably or not is a matter of opinion, by the "Ooniston Flags" of Professor Sedgwick, consisting of about 2,000 feet of cleaved flags, mostly of a very dark grey or black colour. As I have just remarked, the Ooniston Flags were formerly made by Professor Harkness and myself to include the Graptolitic Mudstones; but I am now of opinion that this view cannot be sustained; and it is to the researches of Mr. Hughes that this change in my views is chiefly due. The true relations of the Ooniston Flags, however, are, in my opinion, still uncertain; and I do not think that there is yet sufficient evidence to wan-ant us in asserting positively that they are of Upper Silurian age. Their contained fossils yield very little decisive evidence, consisting chiefly of orthocerata and grap­ tolites. As regards the latter, the most important point is the absence, so far as is yet known, of any diprionidian form. The only species which the Flags contain are Graptolites Sedgwickii, G. priodon, G. colonus, and Retiolites Geinitzianus. Of these, the first three certainly occur in the Graptolitic Mudstones, and there is some evidence of the existence in this formation of even the last. On the other hand, all but G. Sedgwickii are known as characteristic fossils of the Wenlock and Ludlow formations else­ where. The most decisive ground, however, for adopting the view of Mr. Hughes-that the Ooniston Flags belong to the Upper Silurian series-is to be found in the fact that the Flags un- PROF. H. A. NICHOLSON ON THE LAKE DISTRICT. 113 doubtedly pass upwards with entire conformity into the series of the Coniston Grits; and his discoveries leave no room for doubt as to the Upper Silurian age of this latter group. Upon the whole, therefore, the balance of evidence at present seems to be in favour of the view that the Coniston Flags truly appertain to the Upper Silurian Series.

VI. CONISTON GRITS. The Coniston Flags graduate upwards into a great series of grits, slaty, shaly, and arenaceous beds, originally termed the "Coniston Grits" by Professor Sedgwick. As just mentioned, the discoveries of Mr. Hughes have rendered it certain that the Conis­ ton Grits are of Upper Silurian age. This is shown by the occur­ rence of such forms as Spirorbis Lewisii, OrthocerasLudense, Cera­ tiocaris M urchisoni, Beyrichia Kloedeni, Phacops Doumiuqii», and Rhynchonella navicula. There are also grounds for believing that the Coniston Grits are not to be placed very low down in the Upper Silurian series; but their correlation with the type-series of Wales is still uncertain. Under any circumstances no more im­ portant step in unravelling the complicated Silurian series of the Lake District has been made of late years than the discovery that the Coniston Grits are of Upper Silurian age.

VII. KENDAL ROCKS. The Coniston Grits, finally, are succeeded by a great series of shales, grits, and flags, which are largely developed in the neigh­ bourhoood of Kendal, and may therefore appropriately retain the local name of the "Kendal Rocks." The thickness of these beds is very great-apparently not less than four or five thousand feet -and they contain nnmerous fossils of the ordinary Ludlow type. There is, therefore, no hesitation in regarding the Kendal Rocks as being of Upper Silurian age, and as corresponding with the Ludlow Rocks of Wales. If, however, we are to admit that the Coniston Grits and Coniston Flags are likewise of Upper Silurian age, we have to allow that the Upper Silurian series of the North of England has the unprecedented thickness of at least ten thousand feet -more than double the thickness of the Upper Silurians of" Siluria." And if, as seems probable, the Coniston Grits are referable to the Ludlow rather than to the Wenlock, then we shall have to admit 114 EX CURSI ON TO BROMLEY. that the Ludlow formation of the north of England has the enor­ mous thickness of about eight thousand feet, th e corresponding strata in Wale s not reaching a thi ckness of two th ousand feet. W e may confidently expect, however, that future discoveries will enable us to reason with greater cert ainty on these and other similar point s which now are more or less obscure.

EXCURSION TO BROMLEY AND CHISLEHURST. J UNE 1 5 TH, 1872.

D irectol's.-JAM Es W. H.OTT, Esq., and COLES CHILD, E sq., F. G.S. This excursion was rendered noteworthy by the large at tendance of Members, who quite filled the railway station at Shortlands, at which place the party left the tr ain in order to visit the neighbour­ ing West Kent W ater W orks, where a well had recently been sunk into the Chalk. The well had been completed with highly successful results, 'a most abundant supply of excellent water having been obtained. The resident engineer, Mr. Morris, kindly described the operations, and exhibited a detailed section of th e well. "Valking along the railway the Members attentively examined the sections of the P ebble-beds of th e W oolwich Series, near Bromley Station, and th en entered the park of Bromley P alace, the residence of Mr. Coles Child, and under that gentl eman's gui dance inspected a section of the Shell-be ds of th e 'Woolwich Series, ex­ posing a bed nearly entirely composed of Cyrena, with another bed made up of Ostrea. Mr. Child hospitably entertained the party in th e beautiful gar­ dens of the Palace, in which some of the evergreens are of remarkable size, and th en led the way to his brick-works at Wid more, where an interesting section of th e W oolwich Series with a capping of what may represent the Basement -bed of the London Clay is exposed. Th e lower beds have yielded plant remains in a fine state of preser­ vation. A pleasant walk through Snndridge Park brought the party to the well-known section of the Woolwich Series in the woods of thi s beautiful domain, in which th e Cyrena and Ostrea are found together, and not in separate beds as at the section previously mentioned. The lodge at the park gates is built of mat erial from th ese beds, and the abund ance of fossil shells displayed gives to the structure a very curious and picturesque appearance.