.,74 CAMBRIAN AND SILURIAN IN EUROPE. [XV. 



has been adopted by Lyell. (Proc. Brit. Assoc. for 1868, p. 

 68, and Lyell, Student's Manual of Geology, 466 - 469.) 



Both Phillips and Lyell give the name of Upper Cambrian 

 to the Lingula flags and the Tremadoc slates, which together 

 constitute the Middle Cambrian of Sedgwick, and concede the 

 title of Lower Silurian to the Bala group or Upper Cambrian 

 of Sedgwick. The same view is adopted by Linnarsson in 

 Sweden, who places the line between Cambrian and Silurian 

 at the base of the Llandeilo or the second fauna. It was by 

 following these authorities that' I, inadvertently, in my address 

 to the American Association for the Advancement of Science 

 in August, 1871, gave this horizon as the original division 

 between Cambrian and Silurian.* The reader of the first part 

 of this paper will see with how much justice Sedgwick claims 

 for the Cambrian the whole of the fossiliferous rocks of Wales 

 beneath the base of the May Hill sandstone, including both 

 the first and the second fauna. I cannot but agree with the 

 late Henry Darwin Rogers, who, in 1856, reserved the designa- 

 tion of " the true European Silurian " for the rocks above this 

 horizon. (Keith Johnson's Physical Atlas, 2d ed.) 



The Lingula flags and Tremadoc slates have been made the 

 subject of careful stratigraphical and palaeontological studies by 

 the Geological Survey, the results of which are set forth by 

 Ramsay and Salter in the third volume of the Memoirs of the 

 Geological Survey, published in 1866, and also, more concisely, 

 in the Anniversary Address by the former to the Geological 

 Society in 1863. (Geol. Jour. (19), XVIII.) The Lingula 

 flags (with the underlying Menevian, which resembles them 

 lithologically) rest in apparent conformity upon the purple 

 Harlech rocks both in Pembrokeshire and in Merionethshire, 

 where the latter appear on the great Merioneth anticlinal, long 

 -i !!' pointed out by Sedgwick. The Lingula flags, (including 

 the Menevian) have in this region, according to Ramsay, a 

 thickness of about 6,000 feet. Above these, near Tremadoc 

 and Festiniog, lie the Tremadoc slates, which are here overlaid, 

 in apparent conformity, by the Lower Llandeilo beds. At a 



Since corrected in the reprint of that address in the present volume. 



