CAMBEIAN AND L0WEE SILTJEIAN EOCKS. 557 



that many intermediate forms did not reach, the western areas. 

 Many forms, as they fulfilled their mission, were lost on the way ; and 

 it is only the stronger and more marked varieties, which we now 

 look upon as species, that were able to pass on. Minor changes may 

 also have taken place even in very limited areas ; hut it is evident 

 that the more marked species were tolerably persistent and became 

 more generally distributed. 



The conclusions to be drawn from the foregoing remarks are these : — 



1. That a prse- Cambrian continent extended over all the area now 

 known as Europe, and that it probably reached considerably further 

 to the west and north than it does at present, that this continent 

 had a general inclination towards the south-west, and that there 

 was a difference of level of at least 15,000 feet between the extreme 

 north-east and the south-west. 



2. That the submergence of this continent was gradual, and that 

 the waters encroached from the south-west. 



3. That the eastern portions of the continent did not become sub- 

 merged until after the whole of the Cambrian (Longmynd, Menevian, 

 Lingula-flag and Tremadoc groups) had been deposited over the 

 western areas, and that dry land continued probably to the beginning 

 of the Devonian epoch in the more extreme eastern frontiers, in Asia. 



4. That the migrations of the marine faunas were from the south- 

 west, where oceanic areas prevailed. 



5. That the earliest faunas which reached the European continents 

 indicated a lower type of organic life than those which succeeded 

 them, and that each successive fauna seemed to indicate a higher 

 state of progression, the lowest invertebrates appearing first, and 

 the higher groups not until several preceding faunas had appeared, 

 — this being more marked in the western than in the eastern areas, 

 as many forms had probably ceased to exist by the time the waters 

 had reached the eastern areas. 



EXPLANATION OF PLATE XXVII. 



Outline map of Europe, showing the comparative thickness and depth of 

 deposition of the Cambrian and Lower Silurian rocks in different areas. The 

 comparative depth of water in which the deposits were probably formed is 

 indicated by the depth of tint in the sections. 



Section A. Central regions of Spain (Guadarrama, Montes de Toledo, Pro- 

 vince of Leon, Daroca, &c). 

 „ B. Wales, North and South. For the most part this also represents 



the succession in France (Brittany &c). 

 „ C.Sardinia. The succession here has not yet been thoroughly worked 

 out ; but this section appears to represent generally the con- 

 ditions observed here and also on the south coast of the Medi- 

 terranean (Algiers &c). 

 „ D. Bohemia and Bavaria. 

 ,, E. Norway and Sweden (neighbourhood of Christiania, Lake Wenner, 



&c). 

 „ F. West coast of Russia (Finland and neighbourhood of St. Peters- 

 burg). 

 „ G-. Podolia. 



„ H. Shore of the Arctic Sea (region of Petschora &c). 

 „ I. Ural Mountains. 



