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NATURE 



241 



THURSDAY, JULY 10, 1890. 



LIFE OF SEDGWICK} 



II. 



The Life and Letters of the Reverend Adam Sedgwick, 

 LL.D., D.C.L., F.R.S., Fellow of Trinity College, 

 Cambridge, Prebendary of Norwich, Woodwardian 

 Professor of Geology, 1818-73. By John Willis Clark, 

 M.A., F.S.A., and Thomas McKenny Hughes, M.A., 

 F.R.S. Two Volumes. (Cambridge: University Press, 

 1890.) 



THE main results of Sedgwick's geological work, as 

 stated in these volumes, are briefly as follows. 

 Passing over several contributions, often of permanent 

 value, to the geology of the crystalline rocks of Cornwall 

 and of the Carboniferous system, especially in the north 

 of England, we come first to his monograph on the Mag- 

 nesian Limestone and lower portion of the New Red 

 Sandstone series. Of this Prof. Hughes justly says : 

 '■ It is at once broad and minute : broad in its general- 

 izations — for it places in order a complex group of rocks, 

 which, until it was written, were in complete confusion ; 

 and minute in working out, through the whole of the 

 district selected, from Nottingham to the southern 

 extremity of Northumberland, the boundaries of the 

 different formations and their relations to each other." 

 We are not, however, prepared to follow Prof. Hughes, 

 if we understand him rightly, in his objection to the 

 name Permian as designating thelower part of this series, 

 for the break between that formation and the so-called 

 Trias is probably more important than at first sight 

 appears, and New Red Sandstone is a name obviously 

 provisional. 



Sedgwick undertook a task of unusual difficulty in 

 investigating the rock masses which enter into the 

 " Cumbrian mountains," and ascertaining their relations 

 with the strata in adjacent regions, but it was so success- 

 fully accomplished that subsequent observers have made 

 few if any important changes, though of course they have 

 amplified many details, in his results. 



His work also among the Palaeozoic rocks in Devon- 

 shire and Cornwall, in which, after a time, he was joined 

 by Murchison, was a long and arduous task, at first 

 productive of much controversy. In this, others, as it is 

 said, " helped with facts or with useful criticism," but it 

 seems a fair statement of the result to say that " the now 

 received classification of the Devon rocks remains as 

 Sedgwick and Murchison left it : Culm measures 

 (Carboniferous) above and Devonian below ; the base 

 of the Devonian being there unknown." 



Sedgwick's work in Wales commenced in the year 

 1831. It was a task from which the boldest geologist 

 might well have recoiled. The country was comparatively 

 difficult of access, the maps were not good, little help was 

 to be obtained from palaeontology ; the " grey wacke " 

 rocks were a vast terra incognita. But the "stiffer" the 

 problem, the greater its attraction for Sedgwick. In 



' Continued from p. 219. 



NO. 1080, VOL. 42] 



that and the following years he unravelled the compli- 

 cated structure of North Wales, and placed in order the 

 great rock masses, from the base which he established 

 in the neighbourhood of the Menai Straits, under the 

 great group named after the town of Harlech, to the top 

 of that which he called the Bala group, clearly distin- 

 guishing the latter from the Denbigh Grits and other 

 1 rocks, which are now universally recognized as Silurian. 

 ) Of this part of Sedgwick's work. Prof. Hughes gives 

 , a lucid history, of which the following is a brief outline. 



Sedgwick spent the summer of 183 1 in North Wales, and 

 I established the succession of the rocks from his base line 

 I upwards, across Snowdon and the Merionethshire axis. 

 ; Short accounts of his results were laid before the Cam- 

 I bridge Philosophical Society and the British Association 

 in June 1832. Next month he sent from Wales sections 

 which illustrate the stratigraphical succession from the 

 [ Menai Straits to the Berwyns. Thus, to quote Prof. 



Hughes's words : — 

 ] 



"Sedgwick, by 1832, had explained the geological 

 structure of North Wales ; had sketched out the leading 

 subdivisions of the Cambrian rocks, and had established 

 the correct sequence of the Arenig and Bala series, and 

 placed them in true relation with what were afterwards 

 known as the Silurian (Upper Silurian of Murchison) in 

 Central Wales and the borders." 



Later in the autumn of this year we find that he " had 

 ascertained the exact position of the Wenlock limestone 

 south of Llandovery," and drawn a rough section, 

 " correct as far as it goes," from the Lower Bala beds, in 

 the valley of the Towy, to the Old Red Sandstone. Fur- 

 ther communications, as the result of this prolonged 

 labour in the field, were laid before the British Association 

 and the Cambridge Philosophical Society in 1834. From 

 time to time during the next twelve years important de- 

 tails were worked out ; perhaps the most marked advance 

 being made in the difficult region of Central Wales, 

 between the Towy and the sea, where Sedgwick suc- 

 ceeded in establishing the general succession of the 

 strata, obscure and almost unfossiliferous as they are. 

 In 1 85 1 he practically proved that the name Caradoc 

 which had been used by Murchison in "The Silurian 

 System" (published in 1839, from work begun in 1831) 

 must cover two distinct groups, one containing Bala 

 fossils, the other clearly underlying the Wenlock group, 

 with fossils similar to those in the latter, but without 

 those characteristic of the former. This is actually 

 demonstrated in a paper published in 1852. 

 ; Soon afterwards began, at any rate openly, the difference 

 I regarding the limits of the Cambrian and Silurian systems 

 1 which unhappily estranged him from his friend and from 

 I the Geological Society. The immediate cause appears to 

 I have been the publication, by the Geological Survey, of 

 I a map of North Wales, on which the colours used to 

 I distinguish Silurian rocks were extended over a large 

 part of those hitherto described by Sedgwick as Cam- 

 brian. Why this was done, it is now difficult to under- 

 stand. Between the base of the Cambrian and that of 

 the Old Red only one well-marked physical break exists — 

 that at the base of the May Hill Sandstone (Upper Llando- 

 very). Below this is only a palaeontological break, which 

 at that date had not been clearly recognized. Accordingly, 



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