WALCOTT.] EUROPE. 373 



various formations referred to the Cambrian in North America and 

 Europe; they all fall within the limits of the group and, united, consti- 

 tute a great geologic division of equal taxonomic value with Silurian 

 (Ordovician), Silurian, Devonian, etc. 



COMPARISON WITH THE CAMBRIAN ROCKS OF OTHER COUNTRIES. 



EUROPE. 



Dr. Henry Hicks expresses the view that the sediments of the Cam- 

 brian and Silurian were largely deposited on the western side of the 

 European continent. 1 In Spain and Wales the sediments accumulated 

 to a great thickness, while to the eastward, in Bohemia, Scandinavia, 

 and Kussia, the sections show less than one- fifth of the thickness of 

 those in Wales. In central Russia the Cambrian strata entirely dis- 

 appear and the Silurian (Ordovician) rests unconformably and directly 

 upon the Archeaa. These observations lead to the conclusions (a) that 

 the Cambrian sediments were deposited upon a gradually sinking coast 

 line ; (b) that the greatest depression was on the western margin of the 

 continent ; (c) that the movement which depressed the North American 

 continent during pre-Cambrian time also affected the western side of 

 the European continent, with a gradually diminishing force, from the 

 Atlantic coast to the Ural Mountains. 2 



A comparison of the Atlantic Coast Cambrian series of America with 

 the Atlantic Coast series of Europe, as exhibited in Wales, shows a 

 marked similarity between the sedimentation of the opposite sides of 

 the Atlantic. The basal Cambrian in South Wales, named the Caerfai 

 group, by Dr. Henry Hicks, consists of 1,570 feet of strata, as follows: 

 520 feet of conglomerates and greenish sandstones subjacent to a bed 

 of red shales and schists, 50 feet in thickness, above which 1,0.00 feet 

 of purple sandstones occur. Dr. Hicks correlates the roofing slates of 

 North Wales as found at Llanberris, Bethesda, and Penrhyn with this 

 lower division of the Cambrian, on stratigraphic evidence, as the few 

 fossils found are not sufficiently characteristic to correlate the two 

 series with each other or with the American Lower Cambrian. A com- 

 parison of the sections with that of the southeastern coast of Newfound- 

 land shows in each the presence of a basal conglomerate subjacent to a 

 series of purple and green shales or slates. It is also to be noted that 

 the Lower Cambrian of New Brunswick and eastern Massachusetts is 

 made up of shales of a somewhat similar character to those of the Caer- 

 fai group. It is a curious coincidence that the section of the Lower 

 Cambrian of North Wales is almost identical in the physical character 

 of its slates, including color and texture, to the Lower Cambrian roof- 

 ing slate belt of southern Vermont and eastern New York. 



1 On the deposition of the Cambrian and Lower Silurian rocks. Quart. Jour. Geol. Soc, London, vol. 

 81, 1875, PI. 27, op. p. 558. 



2 Walcott, C. D. : The fauna of the Lower Cambrian or Olenellus zone. 10th Ann. Rep, U. S. Geol. 

 Surv., 1890, pp. 563, 564. 



