CHAP. II.] CAMBRIAN PERIOD. 23 



upon the result of the first condensation of water upon the 

 earth's surface, and was the Cambrian sea the first great 

 body of water that ever lay over the European area ? It 

 must be admitted that there are some grounds for so think- 

 ing ; there may have been lower levels and older oceans in 

 other parts of the world, but so far as we know the Cam- 

 brian rocks are the oldest aqueous deposits in Europe, and 

 the Caerf ai beds of South Wales contain the oldest remains 

 of invertebrate animals ; moreover, though these animals 

 are certainly the ancestors of modern marine species, the 

 waters of the Cambrian sea may not have been salt ; and 

 we have no proof that these creatures had been differen- 

 tiated into salt- and fresh-water forms until we reach the 

 close of the Devonian period. 



Dr. Hicks has discussed the general geographical condi- 

 tions of the Cambrian period, 1 and he thinks that the 

 higher parts of the pre-Cambrian land lay toward the 

 north-east of Europe, and that the surface had a general 

 slope from north-east to south-west, but was traversed by 

 mountain ridges having a general E.N.E. and W. S.W. 

 direction. If this were so, and subsidence took place, 

 the part of the surface which faced south-west would 

 first become covered by the sea. He infers from a consi- 

 deration of the Cambrian series in various parts of Europe 

 that the sea gradually spread further and further to the 

 north-east, and that there was a difference in level of 

 15,000 feet between the low ground of the south-west and 

 the high ground in Russia. 



The late Professor Linnarsson, however, entirely differed 

 from Dr. Hicks. He points out 2 that the Scandinavian 

 succession goes nearly, if not quite, as low as that of South 

 Wales, and further that, though the sandstones below the 

 Scandinavian Menevian are not so thick as the British, this 



1 " Quart. Journ. Geol. Soc.," vol. xxxi., p. 552. 



2 " Geol. Mag./' 1876, p. 145. 



