318 GEOLOGY. 



peaks of the west date from this time, or later. The building of these 

 cones appears to represent the later phase of the prolonged period of 

 volcanic activity, just as the great lava flows and intrusions represent 

 the earlier. Lesser cones in many places are probably to be referred 

 to the same period. 



Foreign. 



From considerable areas of Europe covered by water during the 

 Miocene, the waters retreated late in the period, or at its close. The 

 sea still covered 'some parts of the continent, and at some points it 

 extended itself at the expense of the land. Southern and southeastern 

 England, Belgium, and perhaps a little of northern and parts of western 

 France, were under water during at least some part of the Pliocene, 

 but the submergence was not everywhere continuous from the Mio- 

 cene, for the Pliocene sometimes (some parts of Belgium) rests with 

 well-developed unconformity on Miocene and older beds. The sea 

 covered much more extensive areas of the present continent about 

 the Mediterranean, where parts of southern France (Rhone basin 

 as far north as Lyons), Spain, Italy, Sicily, and Greece, were still 

 submerged. Beyond the inland margins of the marine Pliocene, there 

 are beds of lake or river origin. In southeastern Europe, brackish and 

 salt lakes came into existence, as shown both by the fossils and the 

 local deposits of salt and gypsum. In other places, sedimentary deposits 

 were made in fresh lakes and river valleys, and in both, remnants of 

 terrestrial life are found. Locally (Turkey), naphtha is said to be derived 

 from the Pliocene. 1 



The beds deposited at this time show a culmination of the ten- 

 dency to local variation characteristic of the Tertiary. This was the 

 necessary result of the separation and isolation of the areas of depo- 

 sition. 



In England the lower part of the Pliocene is marine, and the upper 

 part lacustrine, fluvial, and pluvial, as if the sedimentation shut out 

 the sea. The system here attains a maximum thickness of between 

 100 and 200 feet. Here belong the beds known as Coralline Crag, 

 Wealden Crag, Norwich Crag, Chillesford Crag, and Weyburn Crag, 

 names applied to layers often no more than 10 feet in thickness. 



1 English, Q. J. G. S., 1902, p. 80, and 1904, p. 265. 



