HISTORICAL GEOLOGY 95 



The Silurian Controversy. 



Just as in America the base of the Paleozoic was 

 involved in a protracted controversy, so in England the 

 Cambrian-Silurian succession was a subject of long 

 debate between Sedgwick and Murchison, and among the 

 succeeding geologists of Europe. The history of the 

 solution is so well and justly stated in the Journal by 

 James D. Dana under the title "Sedgwick and Murchi- 

 son: Cambrian and Silurian" (39, 167, 1890), and by Sir 

 Archibald Geilde in his Text-book of Geology, 1903, that 

 all that is here required is to briefly restate it and to 

 bring the solution up to date. 



Adam Sedgwick (1785-1873) and B. I. Murchison 

 (1792-1871) each began to work in the areas of Cam- 

 bria (Wales) and Siluria (England) in 1831, but the 

 terms Cambrian and Silurian were not published until 

 1835. Murchison was the first to satisfactorily work out 

 the sequence of the Silurian system because of the 

 simpler structural and more fossiliferous condition of 

 his area. Sedgwick, on the other hand, had his academic 

 duties to perform at Cambridge University, and being an 

 older and more conservative man, delayed publishing his 

 final results, because of the further fact that his area 

 was far more deformed and less fossiliferous. In 1834 

 they were working in concert in the Silurian area, and 

 Sedgwick said: "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 every- 

 thing which he then taught me. . . . The whole ' Silurian 

 system' was by its author placed above the great undu- 

 lating slate-rocks of South Wales." At that time Mur- 

 chison told Sedgwick that the Bala group of the latter, 

 now known to be in the middle of the Lower Silurian, 

 could not be brought within the limits of the Silurian 

 system, and added, ' ' I believe it to plunge under the true 

 Llandeilo-flags," now placed next below the Bala and 

 above the Arenig, which at the present is regarded as at 

 the base of the Ordovician. 



The Silurian system was defined in print by Murchison 

 in July, 1835, the Upper Silurian embracing the Ludlow 

 and Wenlock, while the Lower Silurian was based on the 



