March 6, 1890] 



NATURE 



421 



soon be published. Whatever may ultimately prove to 

 be the true nature of the molecular change which accom- 

 panies the thermal treatment of iron and determines its 

 mechanical properties, there is little doubt but that there 

 is a close relation between the action of foreign elements 

 and their atomic volume. F'ew metallurgial questions 

 are of greater interest at the present time than those 

 which relate to the molecular structure of metals, and the 

 admirable work of M. Osmond has shown it to be very 

 probable that the presence of a small quantity of a foreign 

 metal may cause a mass of another metal to pass into an 

 allotropic state. In relation to iron and steel the problems 

 are of great industrial importance, and it is fortunate 

 that we appear to be nearing the discovery of a law in 

 accordance with which all metallic masses are influenced 

 by " traces." W. C. Roberts- Austen. 



SEDGWICK AND MURCHISON : CAMBRIAN 

 AND SILURIAN?- 



ERRONEOUS impressions have long existed among 

 American geologists with regard to the relations to 

 one another, and to Cambrian and Silurian geology, of 

 Sedgwick and Murchison. The Taconic controversy in 

 this country served, most unreasonably, to intensify feel- j 

 ings respecting these British fellow-workers in geology, 

 and draw out harsh judgments. Now that right views on 

 the American question have been reached, it is desirable 

 that the facts connected with the British question should 

 be understood and justly appreciated. 



Sedgwick and Murchison were literally fellow-workers 

 in their earlier investigations. Prof. John Phillips, in a 

 biographical sketch of Sedgwick (Nature, vol. vii. p. 257), 

 whose intimate friendship through fifty years " he had 

 the happiness of enjoying," speaks thus, in 1873, of their 

 joint work : — 



" Communications on Arran and the north of Scotland, 

 including Caithness (1828) and the Moray Firth ; others 

 on Gosau and the Eastern Alps (1829-31) ; and still 

 later, in 1837, a great memoir on the Palaeozoic strata of 

 Devonshire and Cornwall, and another on the coeval 

 rocks of Belgium and North Germany, show the labours 

 of these intimate friends in the happiest way — the broad 

 generalizations in which the Cambridge professor delighted, 

 well supported by the indefatigable industry of his zealous 

 companion." 



Prof. Phillips then speaks of the Cambrian and Silurian 

 labours " of two of the most truly attached and mutually 

 helpful cultivators of geological science in England." 



Of these Cambrian and Silurian labours it is my purpose 

 to give here a brief history derived from the papers they 

 published. They were begun in 1831, without concert — 

 Sedgwick in Wales, Murchison along the Welsh and 

 English borders. 



In September of 183 1, the summer's excursions ended, 

 Murchison made his first report at the first meeting of 

 the British Association. It was illustrated by a coloured 

 geological map representing the distribution of the 

 ■" Transition Rocks," the outlying Old Red Sandstone, 

 and the Carboniferous limestone (Murchison, Report of 

 the British Association, i. 91, 1831). 



These "Transition Rocks" (of Werner's system), up- 

 turned semi-crystalline schists, slates, and other rocks, 

 passing down into uncrystalline, and regarded as mostly 

 non-fossiliferous, the ^' agnotozoic" of the first quarter of 

 the century, were the subject of Sedgwick's and Murchi- 

 son's investigations— the older of the series, as it turned 

 out, being included in Sedgwick's part^ They were 



' Printed from advance sheets kindly supplied by Prof. Dana. The 

 article appears in the current number of the American Journal of Science. 



^ Murchison says, in the introductory chapter of his ''Silurian System," 

 p. 4, " No one [in Great Britain, before his investigations began] was aware 

 ■of the existence below the Old Red Sandstone of a regular series of deposits 

 containing peculiar organic remains." " From the days of De Saussure and 



early resolved into their constituent formations by 

 Murchison, and later as completely by Sedgwick in his 

 more difficult field.^ 



Already in March and April of 1833, Murchison showed, 

 by his communications to the Geological Society of 

 London, that he had made great progress ; for the re- 

 port says -.'^ — He "separated into distinct formations, by 

 the evidence of fossils and the order of superposition, the 

 upper portion of those vast sedimentary accumulations 

 which had hitherto been known only under the common 

 terms of Transition Rocks and Grauwacke." And these 

 " distinct formations " were : (i) the Upper Ludlow rocks ; 

 (2) the Wenlock limestone ; (3) the Lower Ludlow rocks ; 

 (4) Shelley sandstones, "which in Shropshire occupy 

 separate ridges on the south-eastern flanks of the VVrekin 

 and the Caer Caradoc " ; (5) the Black Trilobite flag- 

 stone whose " prevailing Trilobite is the large Asaphus 

 Buchii, which with the associated species," he observed, 

 " is never seen in any of the overlying groups " ; and 

 below these, (6) Red Conglomerate sandstone and slaty 

 schist several thousand feet in thickness. 



By the following January, 1834, Murchison was ready 

 with a further report,^ in which he described the " four 

 fossiliferous formations" in detail, and displayed, on a 

 folded table arranged in columns, their stratigraphical 

 order, thickness, subdivisions, localities, and " charac- 

 teristic organic remains." The subdivisions of the rock- 

 series in the memoir are as follows, commencing above : 

 (I.) Ludlow rocks, 2000 feet ; (II.) Wenlock and Dudley 

 rocks, 1800 feet ; (III.) Horderley and May Hill rocks 

 (afterward named Caradoc), 2500 feet ; (IV.) Builth and 

 Llandeilo flags, characterized by Asaphus Buchn, 1200 

 feet ; and, below these, (V.) the Longmynd and Gwas- 

 taden rocks, many thousand feet thick, set down as 

 unfossiliferous. 



Thus far had Murchison advanced in the development 

 of the Silurian system by the end of his third year. 

 Upper and Lower Silurian strata were comprised in it, 

 but these subdivisions were not yet announced. 



During the interval from 183 1 to 1834, Sedgwick pre- 

 sented to the British Association in 1832 a verbal com- 

 munication on the geology of Caernarvonshire, and 

 another brief report of progress in 1833. A few lines for 

 each are all that was published. The difficulties of the 

 region were a reason for slow and cautious work. 



In 1834, as first stated in the Journal of the Geological 

 Society for the year 1852, the two geologists took an 

 excursion together over their respective fields. Sedgwick 

 says (Quarterly Journal of the Geological Society, viii. 

 152, 1852) : " I then studied for the first time the Silurian 

 types under the guidance of my fellow-labourer and 

 friend ; and I was so struck by the clearness of the 

 natural sections and the perfection of his workmanship, 

 that I received, I might say, with implicit faith everything 

 which he then taught me." And further, " the whole 

 'Silurian system' was by its author placed above the 

 great undulating slate-rocks of South Wales." The geo- 

 logists next went together over Sedgwick's region, and 



Werner, to our own, the belief was impressed on the minds of geologists that 

 the great dislocations to which these ancient rocks had been subjected had 

 entirely dissevered them from the fossiliferous strata with which we were 

 acquainted." 



The term " Transition " early appeared in American geological writings. 

 Sixty to seventy-five years ago it was applied by Maclure, Dewey, and Eann, 

 to the rocks ot the Taconic region and their contiauation ; for these were 

 upturned, apparently unfossiliferous, semi-crystalline to uncrystalline, and 

 extended eastward to a region of gneisses. The study of the rocks u as com- 

 menced ; but in 1842, before careful work for the resolution of them had been 

 d<ine — like that in which Murchison and Sedgwick were engaged — they were, 

 unfortunately, put, as a whole, into a "Taconic system" of assumed pre- 

 Potsdam age ; at the same time "Transition" was shoved west of the Hud- 

 son, over rocks that were horizontal, and already resolved. Owing to this 

 forestalling of investigation, and partly also to inherent difficulties, the right 

 determination of the several formations comprised in this Tac -nic or "Tran- 

 sition " region was very long delayed. 



2 Murchison, Proceedings of the Geol. Soc. London, i. 470, 474, 1833, in a 

 paper on the sedimentary deposits of Shropshire and Herefordshire. 



3 Murchison, Proc. Geol. Soc, ii. 13, 1834. The subject was also before 

 the British Association ; Report for 1S34, p. 652. 



