99 ORDINARY MEETING, JUNE 7TH, 1872. The Rev. THOMAS WILTSHIRE, M.A., F.G.S., &c., President, in the Chair. The following Donations were announced :- "Memoirs of the Geological Survey of England and Wales," vol. iv., "The Geology of the London Basin," by William Whit­ taker, B.A., F.G.S., from the Author. " Thesaurus Siluricus, the Flora and Fauna of the Silurian Period," by J. J. Bigsby, M.D., F.G.S., from the Author. " Sketch of the Geology of the Neighbourhood of Banbnry," by Thomas Beesly, F.C.S., from the Author. " Report for 1870 of the Geological Survey of Ohio," from the Ohio State Survey. "Thirty-ninth Annual Report of the Royal Cornwall Polytechnic Society, 1871," from that Society. "Quarterly Journal of the Geological Society," from that Society. " Abstract of the Proceedings of the Geological Society," from that Society. "Proceedings of the South Wales Institute of Engineers," from that Institute. The following were elected Members of the Association :­ George Blumberg, Esq.; James Campbell, Esq.; William Chapple, Esq.; Edwin Litchfield, Esq.; Samuel Rowles Pattison, Esq., F.G.S.; Mrs. Robins; Miss Jane C. Seel; W. T. Stone, Esq.j Thomas Warburton, Esq. ; and Cecil Ray, Esq. The following Papers were read :- 1. ON THE CLASSIFICATION OF THE CAMBRIAN AND SILURIAN ROCKS. By HENRY HICKS, Esq., M.R.C.S., F.G.S. Geological science is so progressive, and new discoveries are so frequently made, that it can scarcely be expected that the classifi­ cation of any portion of the series of stratified rocks can re­ main long without the necessity for considerable change and modification: the classifications, therefore, of the Cambrian and Silurian Rocks, by Professor Sedgwick and Sir R. Mur­ chison, made many years ago, and sufficiently correct at that H 100 H. HICKS ON CAMBRIAN AND SILURIAN CLASSIFICATION. time, are now in several respects unsatisfactory. Even at pre­ sent, when so much still lies hidden from our view in unexplored regions, any attempt at a classification must be more or less im­ perfect, though it is satisfactory to find that fresh discoveries leading towards a natural arrangement are continually being made. Systems of classification are necessary, if only for working pur­ poses, and doubtless cannot be dispensed with on that account j still, it must not be forgotten that all lines of division, wherever placed, are more or less arbitrary, for we have only one great natural system to deal with, and, therefore, as Nature from time to time unfolds herself to us, so these lines have to yield and give way to others. Weknow also thatthere are numerous breaks in the succession even at present, and we avail ourselves of these accidental circumstances frequently for purposes of classification; but as these have arisen chiefly from faults in the strata, denudation, and such causes, we must expect to be able to fill up many of these gaps as our know­ ledge of hitherto unexplored and imperfectly explored regions becomes more satisfactory. It is important also to bear this fact in mind in examining the organic remains of succeeding groups; for, however dissimilar the forms in these groups may appear, this must not be looked upon as a want of accord in nature, but as evidence only of the absence, by some accidental cause, of deposits, which, had they been present, would have shown how unvaryingly true Nature has always been to her laws. In the accompanying Table the groups of strata which are known, collectively, to form at present the Lower Paleeozoio rocks of this country are placed in their natural order of succession; and side by side the classifications of these groups, as adopted by Professor Sedgwick, and by Sir R. Murchison, along with the one nowproposed. All rocks not newer than the Bala Limestone were placed by Professor Sedgwick in his Cambrian, which was divided by him into an Upper, Middle, and Lower portion; the Upper consisting of the Bala group, and the Arenig or Skiddaw group; the Middle, of the Tremadoc, and Ffestiniog groups; and the Lowe?', of the Harlech, and Longmynd or Bangor groups. His Silurian included the beds from the base of the May Hill group to the top of the Downton Sandstone, the Bone Bed, and Upper Ludlow. By Sir R. Murchison, the Cambrian was made to include only H. HICKS ON CAMBRIAN AND SIL URIAN CLASSIF IC ATION. 101 th e beds contained in Professor Sedgwick's Lo wer Cambrian, viz., th e Longmynd or Bangor group, and the Harlech group, the whole series above th ese being ' called Silurian, or rather, in his most recent work, P rimordial S ilurian and Silurian, the name P rimordial S ilurian being adopted by him after the publication of th e researches by Mr. Salte r and myself in the Menevian group in W ales. Murchison's classification varied considerably from time to time (the last being th at published in "Siluria," in 1868, and which corresponds with th e one in th e Table), and apparently not so much with a view to a more natural arrangement as to include all fossili­ ferous rocks of th e early formations in his Silurian, leaving the term Cambrian only to what he in 1868 called th e sterile bases of th e fossiliferous rocks; th ese" sterile bases," however, even in that year proved to be them selves richly fossiliferous. Th e divisions now proposed differ in several particulars from those of Professor Sedgwick, and Sir R. Murchi son, and are an attempt at a more natural arrangement in accordance with P alreontological evidence. This arrangement has alr eady been adopted to a great extent by Sir Charles Lyell, in his " Student's Manual of Geology," 1871, and by Mr. SaIter and myself in several papers. r have left out from th e Table the rocks which of late years have become known to us under the names p re-Cambrian or Laurentian, as they have yielded no organic remains at present in th is country. Moreover, th eir position is easily recognised, and no difficulty is likely to occur with th em. They appear generally as quartzifcrous or g ranitic rocks, with a st rike from N.W . to S.E., and, hence, discordant to that of the overlying Cambrian stra ta, which invariably in this country has a strike from about N.E. to S.W. These p re-Cambrian rocks occur as ridges in the strata in th e neighbourhoods of St. David' s, and Malvern, Charnwood F orest, the H ebrides, and western parts of Scotland. In the Table the lowest gro up is the Longmynd, so named from the Longmynd hill s of Shropshire. This group is usually divid ed into an upper and a lower portion, the former sup­ posed to be equivalent t o th e Harlech Grits, and th e latter to the Ll anberis Slates. There is no evidence, however, at present t o show that th e Ll anberis Slates are older than the Harlech Grits , for the difference in th eir lithological characters may easily 102 H. H ICK S ON CAMBRIAN AND SIL UR IA N CLAS BIF IC ATION. W en be explained, as stated by Sir C. Lyell, w by lookin g upon them as deposits of fine mud thrown down in th e same sea, on the borders of which the sands of the Harlech Grits were accumulating. The great thickness of the strata in the Longmynd hills has na turally led authors to believe in th e probability of a more ancient series occurring there than is present in th e H arlech district, but this view seems not borne out by actual facts , ~ sinee there is every probability of repeti- ~ ti ons of the strata in the L ongmynd dis- === trict, as is the case at St . Davi d's; more- ::t: over, after an examination of th e beds 0S at these places, I am inclined to believe tr: tn" that in no case does th e actual thickness 8 of the series, without repetitions, attain ~ .-,: to nearly what has been usually given A to it in th e Longmynd hills. The series ~ so well exposed in coast sections at St. ui David's is evidently identical with that 6 in North Wales, and Shropshire; the ~ lith ological cha racters and th e order of z succession being strangely alike, and ;::S ~ even th e thickness, when any particular .:::: series is exposed to view, shows only a ~ o very slight difference. Th e lowest beds ... at St. Da vid's, in my opimon, are cer- 0 ta in!y of equal antiquity to any in th e 13 Longmynd hills, and have the ad vantage t; of showing a base resting on a pre-Cam- @ br ian ridge, such as is nowhere shown in th e Longmynds, or in Nor th Wales. The accompanying section explains the relation of these beds to the pre-Cambrian islands at St. David's. The life of this period, so far as we at present kn ow, consisted of annelids, crus­ taceans, brachiopods, pteropods, and 8ponges. From 3000 to 4000 feet of these beds, in natural succession, ha ve H. HICKS ON CAMBR IA N AND SI LU R IAN CL ASS IF IC ATI ON. 103 yielded fossils at St. David's, where as yet th ey have been chiefly examined. The Longmynd beds in Shropshire, in North Wales, and also in Ireland, have also yielded a few indications of life, but these districts need fur ther exploration.