Chemical and Geological Essays of T. Sterry Hunt 159 



fossiliforous rocks of Wales and the bordering counties of England. 

 He has at length brought his survey of five years to a successful termina- 

 tion ; aiid his work will form a most important step in the progress of geo- 

 logical science, not merely as elucidating the history of a portion of the 

 sedimentary formations of our island, but as fixing the characters of a 

 succession of normal groups, to which the strata of other parts of 

 Europe, and perhaps of America, may be referred. A large, and 

 beautifully illustrated treatise, in which he intends to give a detailed 

 description of his original observations and views, will soon be pub- 

 lished. In the meantime, we have tasted, as it were, by anticipation, 

 the fruits of his labors, having, year after year, received at our meet- 

 ings the earliest intelligence of his discoveries, and having freely 

 discussed and criticised them long before it was possible for him to lay 

 the whole in a matured and digested form before the public. You are 

 aware that the system of rocks, Avhich have been the chief object of 

 his research, constitutes the upper part of Avhat was formerly called 

 the transition or greywacke series. In these strata, which had prev. 

 iously remained m a state of obscurity and confusion, he has distin- 

 guished several formations. The old red sandstone rests conformably 

 on the uppermost of these, while the lowest of them repose both 

 conformably and unconformably on the ancient slate-rocks of 

 Wales. Mr. Murchison proposes the general name of "iSilurian" 

 for this whole system, as the strata studied in those parts of England 

 and Wales once occupied by the ancient British nation, the Silures. 



The necesssity of a new term has arisen from the uncertain latitude 

 with which the word "transition" had been applied— some authors 

 including in it the carboniferous rocks ; and also, from the still greater 

 confusion introduced by the word " greywacke," a term which can only 

 be employed conveniently in a mineralogical sense, to designate a pe- 

 culiar kind of rock which has been formed at many successive epochs. 

 Thus, for example, in the memoir now under review, it Is shown that 

 in Pembrokeshire, grits, which have passed for greywacke, occur in 

 the true coal-measures in the old red sandstone in the Silurian, and in 

 the still older systems of rock. 



Below the Silurian strata are slate rocks of older date, in which 

 traces of organic remains have been agahi detected ; and Prof. Sedg- 

 wick, has suggested the name of Cambrian for this more ancient sys- 

 tem, which is conterminous over a wide territory with the Silurian for- 

 mations, the relative position of both being clearly seen. 



Mr. Murchison has recently traced the Silurian system running in 

 zones through Pembrokeshire, and there rising out in the coast cliffs 

 from beneath the old red sandstone as conformably as in the interior 



