168 J. I). Dana — Sedgwick and Murchison. 



Professor Phillips then speaks of the Cambrian and Silurian 

 labors u of two of the most truly attached and mutually help- 

 ful cultivators of geological science in England." 



Of these Cambrian and Silurian labors it is my purpose to 

 give here a brief history derived from the papers they pub- 

 lished. They were begun in 1831, without concert — Sedgwick 

 in Wales, Murchison along the Welsh and English borders. 



In September of 1831, the summer's excursions ended, Mur- 

 chison made his first report at the first meeting of the British 

 Association. It was illustrated by a colored geological map 

 representing the distribution of the " Transition rocks," the 

 outlying Old Red Sandstone, and the Carboniferous limestone.* 



These " Transition Pocks " (of Werner's system), upturned 

 semi-crystalline schists, slates and other rocks, passing down 

 into un crystalline, and regarded as mostly non-fossiliferous, the 

 lt agnotozoic" of the first quarter of the century, were the sub- 

 ject of Sedgwick's and Murchison's investigations — the older 

 of the series, as it turned out, being included in Sedgwick's 

 part.f They were early resolved into their constituent forma- 

 tions 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 report says :§ He " separa- 

 ted into distinct formations, by the evidence of fossils and the 

 order of superposition, the upper portion of those vast sedi- 

 mentary accumulations which had hitherto been known only 

 under the common terms of Transition Pocks and Grau- 

 wacke." And these "distinct formations" were: (1) the Upper 



* Murchison, Report of the British Association, i, 91, 1831. 



■j- 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 exist- 

 ence below the Old Red Sandstone of a regular series of deposits containing 

 peculiar organic remains." "From the days of De Saussure and Werner, to our 

 own, the belief was impressed on the minds of geologists that the great disloca- 

 tions 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 Eaton to« 

 the rocks of the Taconic region and their continuation ; for these were upturned, 

 apparently unfossiliferous, semi-crystalline to uncrystalline, and exteuded east- 

 ward to a region of gneisses. The study of the rocks was commenced : but in 

 1842, before careful work for the resolution of them had been done — 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 Hudson, 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 Taconic or "Transition" region was very long delayed. 



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

 paper on the Sedimentary deposits of Shropshire and Herefordshire. 



