270 GEOLOGY. 



Foreign Cambrian. 



Europe. 1 — The only continent besides North America which has 

 been sufficiently studied to allow of definite portrayal of the Cambrian 

 formations, is Europe. In the area occupied by this continent there 

 is evidence that there was, as in North America, a somewhat wide- 

 spread deformation in pre-Cambrian time, which converted large areas 

 into land. Further, there is evidence that these lands, like those of 

 America, were subjected to protracted erosion before the deposition of 

 the oldest known Paleozoic formations. As a result, the Cambrian 

 system, where its base is seen, generally rests unconformably on older 

 strata, but in places it is so highly metamorphic as not to be readily 

 distinguished from them. Occasionally, too, there may be real grada- 

 tion into the Proterozoic formations. 



The Cambrian formations of Europe, like those of America, are 

 mainly clastic. They include conglomerates, sandstones, graywackes, 

 shales and their metamorphic equivalents, quartzites, slates, schists, 

 etc. In some places, thick bodies of limestone, partly or wholly meta- 

 morphosed, are associated with the clastic beds. A considerable pro- 

 portion of the material involved in the clastic formations is coarse, 

 and the strata are often ripple-marked, and affected by cross-bedding 

 and by sun-cracks. All these features point to the conclusion that a 

 large part of the Cambrian sediments were laid down in shallow water. 

 In some regions the formations are notably red, a fact which has been 

 thought to indicate that they were formed on land or in lakes or inland 

 seas. 2 



The European Cambrian is notable for its extreme variations in 

 thickness. In Wales (Cambria), the country from which the system 

 received its name, it has a thickness of 12,000 feet or more. 3 This 

 great thickness is equalled or exceeded in Brittany, where formations 

 8000 meters in thickness are referred to the system. In western England 

 the thickness is 3000 feet, and in northern Scotland 2000 feet, while in 



1 The best summary of the Cambrian of Europe, in English, is found in Geikie's 

 Text-book of Geology, 4th ed. , Vol. II. This text gives references to the literature. 

 Other recent summaries are given in DeLapparent's, Traite de Geologie, Credner's 

 Elemente der Geologie, and Kayser's Formationskunde. 



2 Ramsey, Quart. Jour, of the Geol. Soc, Vol. XXVII, 1871, p. 250. 

 3 DeLapparent (Traite de Geologie, 4th ed., 119) assigns the Cambrian of this 



region a thickness of 8000 to 10,000 meters. 



