376 THE CAMBRIAN. [bull. 81. 



inces. In point of fact the Atlantic Coast Province of America is 

 practically a portion of the Atlantic Province of which the sections of 

 western Europe are on the eastern side. The Bohemian area and that 

 represented by the deposits on the island of Sardinia partake, in part, 

 of the character of the Atlantic Basin deposits, in the presence of the 

 Paradoxides fauna, but not in other details. 



The essential difference between the English and the American clas- 

 sification is in drawing the line between the Cambrian and Silurian 

 (Ordovician). The English geologists have included the Upper Tre- 

 madoc slates, with their strongly marked Ordovician fauna, in the 

 Cambrian, because a local strati graphic break occurs at their summit 

 and between it and the subjacent Arenig series. By the definition 

 adopted in this paper for distinguishing the great geologic groups, the 

 Upper Tremadoc slates, with their fauna, would be included in the Si- 

 lurian (Ordovician), and the line of delimitation between the Cambrian 

 and the Silurian (Ordovician) be drawn at the base of the upper Tre- 

 madoc slates, thus referring the Lower Tremadoc and the Lingula flag 

 series to the Upper Cambrian, and the Upper Tremadoc to the base of 

 Silurian (Ordovician). 



In conclusion : (a) The relations between the Cambrian rocks of the 

 eastern or Atlantic coast of North America and those of Wales are of a 

 genetic character, and point to their having been deposited in the same time 

 interval; (b) the Scandinavian Cambrian represents the same interval, 

 but with a greatly diminished bulk of sediments ; (c) the French and 

 Spanish sections are too incomplete for close comparison, although 

 representing the coast of Wales series ; (d) the Bohemian and Sardinian 

 areas point to local conditions that may have affected their connection 

 with the typical Atlantic Basin sediments and faunas. 



SCOTLAND. 



The occurrence of Cambrian rocks in Scotland has not yet been fully 

 proved, but it is quite probable that the Torridon sandstones of north- 

 western Scotland may be referred to the Lower Cambrian. Prof. Ar- 

 chibald Geikie, in summing up the notice of the Cambrian rocks in 

 Scotland in his Text Book of Geology, says : 



In the northwest of Scotland a mass of reddish brown and chocolate-colored sand- 

 stone and conglomerate (at least 4,000 feet thick in the Loch Torridon district) lies 

 unconformably upon the Archean gneiss in nearly horizontal or gently inclined beds. 

 * * * The denudation must have been considerable even in early Silurian 

 times, for the sandstones are unconformably overlaid by quartzites and limestones 

 Containing Lower Silurian fossils, and these younger strata even in the same district 

 rest directly on the Archean gneiss. * * * No trace of organic remains of any 

 kind has been found in the red sandstones themselves, unless certain track-like im- 

 pressions, observed on the west side of Loch Maree, can be regarded as having been 

 imprinted by Crustacea or other organisms. 1 



1 Text Book of Geology, 1885, p. 653. 



