‘T ra n s itio n R o c ks a n d G ra u w a c k e'’一 T h e S ilu ria n a n d C a m b ria n System s through 150 Y ears

by M ichae l B assett

The terms and Cam brian were first published F orm a tiv e S tu dies in a ge o lo gi ca l sen s e in 18 3 5 . Th is a rt ic le r e vi ew s the historical background to the concept and early Sedgw ick and M urchison first m et in the w inter of 1824-25, application of these stratigraph ical division s, and w hen the latter joined the G eological Society of London, their international status after 150 years of being adm itted to m em bership on January 7th, 1825. d ev el op m en 亡。 Sedgw ick had been a m em ber since 1818 and had rapidly becom e a leading figure in the Society, w hich by then w as In tro du ction o ne o f the m a in foru m s fo r th e d iscussio n of sc ie nc e an d philosophy in Britain. A s an authoritative teacher, Sedgw ick D ublin, Ireland, w as the setting for the fifth annual m eeting soon exercised a profound influence on the younger m an, w ho of th e B ritish A ssoc iatio n fo r the A d va nc e m en t o f Sc ie nc e in w as b oth a m b itio us an d d ete rm in ed to m a ke h is m ark o n th e A ugust 1835. O n Friday, A ugust 14th, the R everend P ro- exciting geological developm ents of the early 19th C entury. fessor A da m Sedgw ick and M r. R oderick Im pey M urchison A fter initia l instru ction fro m D e an W illiam B u ck lan d o f (F igs. 1 and 2) read a com m unication to the final session of O xford U niversity, m uch of M urchison's detailed appreciation the G eology and G eography Section entitled "O n the Silurian of field observation and interpretation w as w ith Sedgw ick, and C am brian System s, exhibiting the order in w hich the follow ing the first of their geological excursions together in older Sedim entary Strata succeed each other in E ngland and July 1827. W ales." Sedgw ick read the details of the C am brian rocks as established by his research, w hilst M urchison discussed the B y the late 18201s, the succession of fossiliferous "Secondary" basis for his Silurian stratigraphy; this presentation, by the and "Tertiary" rocks of England (essentially Upper Palaeozoic see m ingly unlikely com bination of a C a m bridge U niversity and younger) w as reasonably w ell established, based on the profe ssor/clergym an and an ex-soldier turned am ateur geol- principles of m apping and faunal superposition dem onstrated ogist, w as the first announcem ent at a form al scientific first by W illiam Sm ith. T o the north and w est, how ever, lay m eeting of the term inology and relationships of the m ajor large tracts of older, supposedly poorly fossiliferous "arena- stratigraphical units that w ere to becom e accepted univer- ceous and slaty rocks" w hose succession and relationships sally as the low er and upper divisions of System rank w ithin r e m a in e d n o t w e ll u n d e rs to o d . T h e s e o ld e r ro c k s w e r e c o m - t h e L o w e r P a l a e o z o ic ro c k s . T he official proceedings of the D ublin m eeting w ere not published until 1836, but two separate reports appeared in 1835, the first being privately printed in D ublin in Septem ber (H ardy, 1835; see also M orrell and T hackray, 1981, p. 185), and the second d istrib ute d to a w ide r sc ie ntific a ud ie nc e in th e D ec e m be r issue o f T h e L on do n an d E dinburgh Philosophical M agazine and Journal of Science (Sedgw ick and M urchi- son, 1835). A lthough the form er account is relatively poorly know n, it constitutes the first form ally published record (on page 107) of the term C am brian as presented by Sedgw ick. In the case of the Silurian System , how - ever, M urchison bad pre-em pted the announcem ent at the D ublin m eeting by publishing a paper in July 1835 entitled "O n the Silurian System of R ocks" (M urchison, 1835). T hroughout their scientific careers M urchison w rote up and prom oted his results m uch m ore rapidly and in greater volum e than Sedgw ick, and although in 18 35 th e tw o w ere c lo se frie nd s and co 卜 laborators, this early publication by M urchison of "his System " w as sy m pto m at- ic o f w h at w as late r to b e co m e the w ell- know n, bitter controversy betw een the tw o 几 gu re 1 : A da m S ed gw ic k Figure 2 : m en (e.g. see T hackray 1976). (1785-1873 ) aged 47. (1792-1871 ) probably aged 55 。

Episodes, Vol. 8, N o. 4, D ecem ber 1985 2 3 1 m only referred to as "T ransition R ocks" or "Transition ture and succession of the rearion. "For a first survev. I (i.e. Series," im plying that they had form ed in a period transi- M urchison) had got the upper grauw acke, so called, into m y tional betw een the earliest chem ical or m olten phases of hands, for I had seen it in several situations far from each earth history and a tim e w hen m ore recognizably m odern other all along the South W elsh frontier, and in Shropshire faunas and floras developed w orldw ide. The old G erm an rock and H erefordshire, rising out conform ably from beneath the nam e "G rauw ack6l' (both w ith and w ithout th e C ontinental low est m em ber of the old red sandstone. M oreover, I had accent) w as also used as an approxim ate synonym of these ascertained that its different beds w ere characterized by "T ransition R ocks," since this general lithological type w as a peculiar ." (G eikie, 1875, pp. 183, 184). substantial com ponent. T hus, in one rem arkable first sum m er, M urchison established In his lecture syllabus at C am bridge as early as 1821, the lithological and faunal control for m ost of his later w ork. Sedgw ick had certainly begun to consider som e of the prob- Such w as the scope of his coverage, that in Septem ber 1831, le m s asso cia ted w ith th e classifica tion o f the o lde r stra tified at the inaugural m eeting of the British A ssociation for the rocks (C lark and H ughes, 1890, pp. 288-290, 533); he had been A dvancem ent of Science held in Y ork, he dem onstrated aw are of them in his native north-w est England fro m boyhood coloured m aps of the "Transition R ocks" that he considered and began to study them seriously there in 1822. It is not to be "a good broad announcem ent of a new step in B ritish difficult to assu m e that he discussed these studies m any " (G eikie, 1875, p. 184).

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Figure 3 : Ludlow and its No rman castle 一 part of F ig ur e 4 : Th e Rh in o g M o u n t a i n s i n t h e H a r l e c h D o m e Murchison 's type Silurian region in the Welsh Border- o f n o r t h - w e s t W a l e s ～ the heart of Sedgwick 's Cam- land . Upper Ludlow rocks in the foreground pass up br ian System ; the rocks ar e m o s tl y co ar s e az en it es o f i n t o D e v o n i a n O l d R e d S a n d s t o n e f a c i e s o f t h e C l e e e ar ly C am b ri an a ge . H i l l s i n t h e d i s t a n c e . tim es w ith M urchison, and by 1831 the tw o had determ ined to M eanw hile, Sedgw ick finally left C am bridge at the beginning unravel the succession in W ales and the adjacent W elsh of A ugust and proceeded to N orth W ales, w here he arrived on Borderland where the 11grauwack611 and associated slaty rocks A ugust 5th, 1831. F or a few w eeks he w as accom panied and are particularly w ell exposed below the O ld R ed Sandstone. helped by the young C harles D arw in, to w hom he taught the rudim ents of geological m apping in a series of traverses A t a tim e w hen the stim ulating scientific clim ate encouraged the ex te nsio n o f Lreo log ical r)rin C iD les in to rela tivelv ; u nk n ow n (Clark and H ughes, 1890, p. 380). In the Caernarvon district of north-w est W ales, w here Sedgw ick concentrated his early territory, it is equ an y im portan t tn a t tn e tw o m e n m u st na ve field w ork, be considered that the "structure is on the w hole acted as catalysts to one another. The problem s w ere con- siderable, but John P hillips, a leading contem porary geolo- regular, and the s竺些e longitudinal," but it was certainly m ore com plex than that encountered by M urchison, and the gist, w as later to em phasize the qualities of the investigators for such w ork ．⋯ "P ractically, before the sum m er of 1831 the area w as only sparsely fossiliferous. A lthough Sedgw ick re- ported good progress in his first su m m er, he felt obliged to w h ole field o f th e a nc ien t ro ck s a n d fossils o f W a les w as stay in N orth W ales rather than attend the B ritish A ssocia- un ex Dlo re cL- bu t th en arose tw o m en 一 Da r n ob ile . o f a ll m en tion m eeting at Y ork, but it was'eventually necessary for him iittea tor tne purpose 一zseagw ick ana m urcluson 一ana sim - to leave the field in O ctober before com pleting his planned ultaneously set to w ork to cultivate w hat had been left a desert" ．⋯ (G eikie, 1875, p. 179). A nother contem porary, program me (Clark and H ughes, 1890, pp. 377-382). W .D . C onybeare, pointed out the practical necessity for these It w as tw elve m onths before Sedgw ick gave the first form al stud ies in com m enting on the 11.... need of a te r m le s s b a r- b a ro u s report of his findings (follow ing his second season's field than grauw acke-slate, w h ic h w o u ld conveniently work) at the second m eeting of the British Association in de no m in a te the ch ara cteristic r o c k o f s era ．⋯，，(G eikie, O xford (Sedgw ick, 1833). L ike M urchison, Sedgw ick dem on- 1875, p. 177). strated the "m ineralogical structure" of his rugged area (Figs. In the late spring-early sum m er of 1831, Sedgw ick w as 4 and 5) with the, aid of m aps and sections, and it is clear that detained on various business in C am bridge, so that M urchison he too had solved m any of the essential problem s of structure set o ut for h is first fie ld seaso n in W ales w ith ou t h is c ol- and succession in his early investigations. league. H e traversed rapidly through south-central W ales and the W elsh B orderland, and w ithin just a few w eeks of his first Surprisingly, the tw o colleagues m ade no attem pt to m arry encounter w ith the "Transition R ocks" (early in June) he their findings at this first form ative stage, and from then on identified abundant fossils below the O ld R ed Sandstone that they continued their field studies independently; the he w as able to trace alonz strike to the L udlow district differences in faunas, lithological succession and structural kr ig. j) ana w nicn gave nim an im m eaiaTe Key to ine siruc- com plexity w ere presum ably too m uch even for them to

2 3 2 Episodes, Vol. 8, N o. 4, D ecem ber 1985 relate initially, and w ithin a few years they w ere each to A lm ost from the outset of his studies, the extent of becom e m ore deeply involved in their ow n detailed problem s. M urchison's am bition and purpose w ere abundantly clear. In T he 1835 announcem ent at D ublin w as to be their only joint a letter of D ecem ber 12th, 1833, to H enry T hom as D e la contribution on C am brian-Silurian geology. B eche, w ho w as later to becom e the first D irector of the G eological Survey, he em phasized that "It is not m erely the R efinem ents and D evelopm ents U pper G rauw acke the relations of w hich I a m desirous of illustrating, but the w hole m ass of strata from the M ountain F rom 1831 onw ards M urchison published a regular series of L im estone dow nw ards w hich part of the Series has in m y reports and papers in w hich the nature, relationships and conscience no developm ent in any part of the w orld equal to detailed subdivision of the "upper G rauw acke Series" w ere set that seen in m v recions (N ational M useum of W ales a r- ou t. In 18 33 h e first u sed the ter m s "L udlo w R o c k" an d chive)." M urchison devoted alm ost all 01 nis energy to trus "W enlock Lim estone," and in 1834 introduced the "H orderley w ork, each sum m er extending the lim its of his m apping, and and M ay H ill R ocks" and "B uilth and L landeilo Flags." T hese recording his field observations w ith detailed notes and w ere the four great divisions of his Silurian System presented sketches; even just after the D ublin m eeting he pushed his in 1835, the first tw o grouped together as "U pper Silurian," boundaries into new areas (Figs. 6 and 7), and by 1837 his w ith the others (now renam ed as the "C aradoc" and field w ork w as essentially com plete. T hrough this period the I'Llandeiloll form ations) com bined in the "Low er Silurian." scope of his Silurian System becam e w ell defined (Fig. 8). B y late 1835, M urchison had obviously form ulated plans to incorporate all his results in a single large book (G eikie, 1875, pp. 231-232), w hich appeared in January 1839. T his volum e, The Silurian System (M urchison, 1839), is a m agnificant com pilation and is the keystone on w hich all subsequent studies of Silurian rocks have been built (Thackray, 1978b). M ost im portantly, it contained abundant descriptions and beautiful illustrations of faunas, w hich im m ediately provided the basis for recognition and correlation of Silurian strata in other regions. M urchison him self played no sm all part in tracing his System 军产一尸 潞彝鬓 m ore w idely. A fter his m onograph appeared, he w as invited 潍 尹卜二 to R ussia in 1840, and returned again in 1841 and 1844. 蒸 These visits resulted in the joint authorship of an equally 鑫麓 热 瓣 鬓舞馨鑫 im pressive m onograph (in 1845) on the Geology 丝 Russia in 毖鬓蓦 笔黔转 撬 (Thackray, 1978a). He also visited Scandinavia in 毅寒馨铆鬓蒸 镰彝藻 羹夔攀 N o r t h W a l e s Figure 5: A r en n i g F a w r i n 一 p a r t o f his w ork by producing it as a sim plified, inexpensive version S ed gw ick 's or ig ina l C a m b r i a n S ys tem (se e a l s o Fi g . 夕）。 Th e ro c k s a r e t l y t uf fs a n d a gg lom e ra te s 刀 0 分 ？竺终s b叩气呼｛少d弊嚷，烈甘lished in four editions between 竺s .L zsz)4 a n o 1 6 (Z k I n U C K r a y , l v o ij . c l a s s i f i e d w i t h i n 石 n e lo we r pa r t o f t h e O r d o v i c i a n S ys tem .

／ 呀呜刁 ;r'，矛./ 皿、，产 产 才 尸 目 式户 蠢撬 r} 护 丫 。，J}.4 f.;,r ﹄ 、 黑 工石花务“ 称 丫 味札、 '/-笋 人 李一 飞 以1 爪 c - 二.V 了 以护 心 冬 叭1 5k -;}_ E 仄介屯 份、 舞生尾 卜 1 丫 补 、． 争 1吨 弋 卜 争 卜 、 争 启‘ 砂 、 A 又 ‘ r J 八 言 、 咖 叭

Figure 6: A page from Murchison 's 1835 field note Figure 7: "Th e Three Chim neys " ， almost vertical book depicting the geology of M arloes Sands in south- sandstone beds of early Silurian (Llandovery) age at west (notebook N74 , Geological Society of M a rl o es S an ds in s o uth -w e st Wa l es ; t h es e b e d s a re L on do n a rch i ve ) 。 shown clearly in th e cen tre of Murchison 's sketch of the section (Fig. 6)．

E pisodes, V ol. 8, N o. 4, D ecem ber 1985 2 3 3 d T he subsequent 25 y e a rs h a v e 丫 Wit- S LL IF ‘t I t J ‘ t ‘ 。‘ n e s s e d s u b s ta n t ia l in c r e a s e s in I I I- ternational cooperation. O ne session 内 of the C openhagen C ongress focussed 殉 on Silurian (and O rdovician) strati- 丫 ：扩乖趁势泄透 ‘ graphy and correlations. In the sam e 氏 . } 1, J I k L 乙，．钾‘厂 工“：‘．矛 year in the U .S.A ., W .B.N . B erry and - 了. d 月 乙 口‘ 女 份丫芍‘ J护 一 ‘尹‘ J 几 口2 公 ‘ 尸 _,r z ‘、．，，二 ，＿ ，了“ ．沪妞 矛 A .J. B oucot began to com pile data 几 for the production of Silurian corre- ‘、 ‘、AL 不 澎品 在奋一‘砂 la tio n c harts for all k no w n area s o f ‘2淤火＿仁朴。。一、、一 outcrop in the w orld; the first of 勺 these charts w as published in 1970 by 巴义忿气亡份叫 石．＿》， the G eological Society of A m erica, V‘ 、1。认 万 ．。，叼 产 and the series is still continuing. 产 W ithout doubt, the scope and scale of ‘，云J ., /, S}, . } - 飞习一‘’‘凡 these charts w as a m ajor factor in 1 encouraging a new global look at the 谁1～、‘ 〔。，、J户 ， ＿‘尸，汀。叼 1 ， I Silurian System . In Septem ber 1971, 价卜 “‘4‘·‘瓜‘· 卜 〔‘，’‘勺‘ a first international sym posium devo- J-1L- ‘一A- ， ted to Silurian geology w as held in 冬 ,7'} ..'- 今 Brest, France (although again in con- 砂＿、奋刀少 ” （21',-,1, /. junction w ith O rdovician specialists). ＿ 山‘二八卜一尹．一成1 Since 1974, the coordination of M an d eflo F orm ation . C aradoe F orm ation . W enlock F orm ation. L u dlow F orm ation . inte rna tio na l e ffo rt has be co m e th e increasing responsibility of the Inte rn atio n al C o m m issio n o n S tra ti- graphy (IC S) w ithin the International U nion of G eological Sciences (IU G S)- 口 .. d 目 . C ara do c S an d itw s . In that year a Subcom m ission on 月ap (g. and i.‘林护." l irne't- 'J WSh}alloe.ch WLie.nleodck. LL.ad-l- ．糯黔 老盘几．谧Oldt Roneed一o f L ow ER S ILU R IA N R oCtis. U P PER SILU RIAN R o cits. Silurian Stratigraphy form ed in Birm ingham , E ngland and began to Figure 8 : An early sketch (above) b y Murchison , tackle the proble m of defining m ajor, globally applicable probably about 1835-36, depicting the subdivision and subdivisions of Series and Stage rank w ithin the Silurian relationships of units in h is Silurian System (Geo- System , and the boundaries betw een them . By 1984 that logical Society of London archive LDGSL859)； this w ork w as com pleted and w as presented to IC S in A ugust at sketch was clearly the basis for the published ver- the International C ongress in M oscow . Follow ing ratification sion (below ) that appeared in h is 1839 book (p ．196)． by IU G S, the results were published form ally last June (B assett, 1985; H olland, 1985). It is appropriate that alm ost exactly 150 years after M urchison first used the term M eanw hile, Sedgw ick w as certainly not idle and continued to Silurian, his "Transition R ocks" should becom e the first attack the older "G rauw acke" in N orth W ales, after 1831. stratigrapbical System for w hich international agreem ent has H is correspondence indicates that he rapidly refined his view s been reached on both the upper and low er boundary levels, on the structure of his region (F ig. 9), but little of the and on a full set of Series and Stage divisions betw een those detailed succession w as published. U nlike M urchison, Sedg- lim its. w ick w as obliged to attend to his acade m ic and ecclesiastical The chronostratigraphical fram ew ork for future studies is duties, and he w as also still very occupied w ith publishing the thus now firm ly established. In 1986 a book w ill be published results of his work in north-w est E ngland. A t the 1835 D ublin that w ill describe in further detail the global standards and m eeting, therefore, the C am brian System w as divided only the basis for this correlation, and in 1989 the Silurian Sub- generally into L ow er, M iddle and U pper groups. com m ission w ill sponsor a second international sym posium (in It w as not until the 1850's that Sedgw ick eventually began to K eele, E ngland) as a m eans of review ing progress over the expand his view s of C am brian geology and classification (e.g. Sedg w ick, 1852). The basis for w ider correlation w as not published until 1855, w hen Sedgw ick's faunas w ere described m onographically by F rederick M 'C oy (Sedgw ick and M 'C oy, 吕〔C 竿tO N I 1855), and by this tim e, of course, M urchison's Silurian System w as w idely recognized and accepted internationally. The problem s of the clear overlap betw een the original C am - brian and Silurian System s w ere not to be resolved until ＼ 热 C harles L apw orth erected the O rdovician System in 1879 宁 (Bassett, 1979). A n Internationally A greed Silurian System 泌卜公子～～2 ＊戒～ 150 years after the birth of the System , Silurian rocks are now know n from every continent except A ntarctica. A lm ost exactly 125 years after the announcem ent at the D ublin m eeting, the term "Silurian" itself w as finally approved 了 刁 internationally, w hen the 21st Session of the International G eological C ongress in C openhagen ruled (23 A ugust 1960) Figure 9 : Sedgwick “ early view of the structure that it should be used for the upper System of the Low er across part of North Wales as dep icted in sections Palaeozoic, taking precedence of the term "G othlandian," dr a wn in a l et ter t o M ur ch is on d at ed J u ly 23 , 1 832 ; w hich had been em ployed w ide巧 in continental Europe fol- the lower section (with Arennig Fawr at left 一 see low ing its introduction (also by M urchison, in 1845) for cor- Fig . 5) overlaps with th e right hand edge of the re la t iv e s tr a ta in S c a n d in a v ia . upper section (from Clark and Hughes , 1890)。

2 3 4 E pisodes, Vol. 8, N o. 4, D ecem ber 1985 next few years. The occasion should prove to be a fitting R efere nc es celebration of the 150 years since the publication of M ur- B assett, M .G ., 1979. 100 years of O rdovician geology. chison's classic volum e on the 旦旦urian 旦lys生em . Episodes, vol. 1979, no. 2, p. 18-21. C ontinuing International Initiatives on the C am brian System Bassett, M .G ., 1985. T ow ards a "com m on language" in C am brian rocks crop out on every continent. Just as the stratigraphy. Episodes, vol. 8, no. 2, p. 87-92. System nam e w as launched in 1835 together w ith the Silurian, so the tw o w ere again linked in international recognition C lark, J.W . and H ughes, T .M c., 1890. The life and letters of the R everend A dam Sedgw ick. C am bridge U niversity Press, w hen the 23 A ugust m eeting in C openhagen of the 1960 vol. 1: p. i-x, 1-539; vol. 2: p. i-vii, 1-640. International G eological C ongress confirm ed the term "C am - brian" for the low est System of the Low er Palaeozoic. G eikie, A ., 1875. Life of Sir R oderick 1. M urchison. John M odern studies of C am brian geology can be regarded as M urray, L ondon, vol. 1: p. i-xii, 1-387; vol. 2: p. i-vi, 1-375. beginning w ith a sym posium on "T he C am brian System , its H ardy, P.D . (publisher), 1835. P roceedings of the F ifth P ala eogeography and the Problem of its Base" held at the M eeting of the British A ssociation for the A dvancem ent of 20th Session of the International G eological C ongress in Science, held in D ublin, during the W eek from the 10th to the M exico C ity in 1956; sponsorship w as by IC S and the Inter- 15th of A ugust, 1835, inclusive. W ith an A lphabetical L ist of national P alaeontological. U nion. A t the 1960 C ongress there M em bers enrolled in D ublin. D ublin, 129p. (+ 13p.) w as a sectional m eeting on C am brian (and late Precam brian) H olland, C .H ., 1985. Series and Stages of the Silurian stratigraphy, and the idea w as first m ooted of form ing a Subco m m ission on C am brian Stratigraphy w ithin IC S. F ur- System . E pisodes, vol. 8, no. 2, p. 101-103. ther steps w ere taken at an inform al m eeting connected w ith M orrell, J. and Thackray, A ., 1981. G entlem en of Science; the next International C ongress in N ew D elhi in 1964, and early years of the British A ssociation for the A dvancem ent of later that year the C am brian Subcom m ission w as "born." Science. C larendon Press, O xford, p. i-xxiii, 1-592. A s w ith the Silurian, the coordination of stud ies directed M urchison, R .I., 1835. O n the Silurian System of R ocks. tow ards the establishm ent of global standards for the C am - L ondon and Edinburgh P hilosophical M agazine and Journal of brian has now beco m e the m ajor responsibility of the Science, vol. 7, p. 46-52. Subcom m ission. Problem s of definition of the base and top of M urchison, R .I., 1839. T he Silurian System , founded on the C am brian System , and of globally applicable internal geological researches in the counties of Salop, H ereford, subdivisions, continue to be m ajor topics of debate w ithin the R adnor, M ontgom ery, C aerm arthen, B recon, Pem broke, Subcom m ission. In 1981 a second international sym posium on M onm outh, G loucester, W orcester, and Stafford; w ith the C am brian w as held in G olden, C olorado, U .S.A ., under the descriptions of the coal-fields and overlying form ations. auspices of the U .S. G eological Survey as part of the Subcom m ission program m e. John M urray, London, part 1: p. i-xxxii, 1-576; part 2: p. 577-768, pls. 1-37. A lthough by 1985 there has been no international agreem ent Sedgw ick, A., 1833. (The geology of Caernarvonshire). on standard C am brian chronostratigraphical subdivisions and R eport of the first and second m eetings of the British boundaries, intensive studies are under w ay throughout the w orld to reso lve c orre latio ns acro ss d ifferen t fac ie s a nd A ssociation for the A dvancem ent of Science; at Y ork in 1831, and at O xford in 1832, (G eology Section), vol. 1833 (for biogeographical realm s. B eginning in 1983, the Subcom m is- 1832), p. 591-592. sion instigated a series of correlation charts (published by IU G S) aim ed at covering all know n outcrop areas, and their Sedgw ick, A ., 1852. O n the classification and nom enclature production holds great prom ise for international agreem ent of the L ow er Palaeozoic rocks of England and W ales. on standards in the near future. A s the bicentenary year of Q uarterly Journal of the G eological Society of L ondon, Sedgw ick's birth, and 150 years after the introduction of his vol. 8, p. 136-168. System , he w ould surely be w ell pleased w ith the continued Sedgw ick, A . and M 'C oy, F ., 1855. A synopsis of the expansion of C am brian investigations m ade through 1985. classification of B ritish P alaeozoic rocks, w ith a system atic A cknow ledgem ents description of the British Palaeozoic fossils in the G eological Mr. John Thackray (G eological Museum , London) and Dr. M useum of the U niversity of C am bridge. J.W . Parker, G eorve SevastODUIO (Trinitv C olleae. D ublin) kindlv Drovided L ondon, vol. 1: p. i-xcviii, i-viii, 1-661; vol. 2: pls. 1A -lL , 2A -2D , 3A-3K . m e w itn in lo rm a tion inc orp orate a in tn is a rticie . ’ Sedgw ick, A . and M urchison, R .I., 1835. O n the Silurian and C am brian System s, exhibiting the order in w hich the older Sedim entary Strata succeed each other in E ngland and D r. M ic ha el G . B a sse tt w a s W ales. T he L ondon and Edinburgh Philosophical M agazine Secretary-G eneral of the IC S fro m and Journal of Science, vol. 7, p. 483-485. 1 9 7 6 t o 1984 and is currently a Thackray, J.C ., 1976. The M u rchison-Sedgw ick controversy. m e m b e r of the C o m m issio n Journal of the G eologic B u r e a u . H e is H ead of the D epart- p. 367-372. m en t o f G eology at the N ational M u s e u m of W ales, C ardiff, U .K ., T hackray, J.C ., 1978a. R .I. M urchison's G eology of R ussia a n d is a V ic e - P r e s id e n t o f T h e (1845). Journal of the Society for the Bibliography of N atural Palaeontological A ssociation. H is H istory, vol. 8, part 4, p. 421-433. rese arch interests are c en tre d o n T hackray, J.C . 1978b. R .I. M urchison's Silurian Syste m P alaeozoic brachiopods, biostra ti- (1839). Journal of the Society for the B ibliography of N atural graphy and facies developm ents, H istory, vol. 9, part 1, p. 61-73. particularly in the U .K . and Sca n dina via . T hackray, J.C ., 1981. R .I. M urchison's Siluria (1854 and later). A rchives of N atural H istory, vol. 10, part 1, p. 37-43.

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