TIIK r.\Mi:i:iAN SYSTEM 105 



total thickness of the Cambrian in Bohemia may be about 3000 

 feet. 



The only other exposure of Cumbrian rocks in Central Europe 

 is in Russian Poland, round Sandomir on the Vistula, where some 

 shales, associated with quart/ates and conglomerates, have yielded 

 sj iceies of Paradoxides (? P. bohemicus), Agnottut (fallax and gibbut), 

 and Liostracus Linnarsoni ; evidently a Middle Cambrian fauna. 



E. EUROPEAN GEOGRAPHY AND CONDITIONS OF DEPOSITION 



Any attempt to restore the geographical conditions of the early 

 Palajozoic periods must be a task of great difficulty. There 

 large areas where the rocks of these early systems are deeply buried 

 below those of newer times, and the exposures which we can study 

 are only so many isolated portions of some ancient sea-floor ; 

 while the traces of contemporaneous lands are only to be found 

 where some series of strata are absent or where coarse detrital 

 deposits are unusually thick. Nevertheless, wherever Pahi-ozoic 

 rocks can be followed over a considerable area some indications of 

 the direction from which the sediment was transported can usually 

 be found, and of the conditions under which it was deposited. 



It will therefore be useful to indicate such evidence as we 

 possess for answering the question under what geographical and 

 physical conditions were the Cambrian strata of Northern and 

 Western Europe accumulated ? 



In the first place, eome general considerations are suggested by 

 a comparison of the deposits in Wales, England, Sweden, and 

 Russia. The enormous thickness of the Welsh Cambrians, which 

 have a maximum thickness of about 11,000 feet, as compared with 

 a possible 3000 feet in Warwickshire, less than 1000 feet in 

 Sweden, and only 680 feet in Russia, is a point of great significance ; 

 but the inference to be drawn from these figures depends on other 

 .-trntigraphical facts. If the lower beds were not represented in tin- 

 Swedish and Russian succession, it might be inferred that the north 

 of Europe was a land-area during the earlier part of the period, and 

 was gradually submerged by the waters of a sea which spread o\vr 

 it from the south-west, and this view was actually suggested in 

 1876 before the Olenellus fauna was recognised in Europe. The 

 facts as we now know them, however, will not allow of such an 

 inference ; the Swedish succession is as complete as that of Warwick- 

 shire or South Wales, and the difference in thickness is caused 

 mainly by the great increase in the amount of sandy material in 

 the Cambrian sediments as we pass from east to west, or rather from 

 north-east to south-west 



