Henry Hicks — On the Northern FalcBOzoic Rocks. 215 



In several future chapters we shall endeavour to trace the succes- 

 sive manifestations of the volcanic forces in the same area, and to 

 show their relations to the tremendous exhibitions of force result- 

 ing in those grand movements by which the Alpine rocks have 

 , acquired their present positions and relations. 



P.S. — I am indebted to my friend, Prof, vom Eath of Bonn, for 

 calling my attention to an error into which I have fallen in the last 

 chapter of this series. On page 54, I have classed the gaseous ex- 

 halations of the Biidos Hegy in Transylvania with those of the 

 Solfatara, al having an elevated temperature. This is not the case, 

 however, the gas evolved at the former locality having the same 

 temperature as the surrounding atmosphere. 



{To be continued.) 



IV. — Some Considekations on the Probable Conditions under 

 which the palieozoic eocks were deposited over the 

 Northern Hemisphere. 



By Henry Hicks, F.Gt.S. 

 {Continued from page 160.) 



Upper Silurian. — At the close of the Lower Silurian, as already 

 stated, changes of considerable importance took place in some of the 

 areas which had undergone depression. The sea-bottom was now 

 raised in parts of Western Europe, and in North America, and islands 

 of some extent formed. In Europe the most important were those in 

 North Wales, Shropshire, Cumberland, the South of Scotland, and in 

 Nassau. It is probable also that one or more extended along Southern 

 Europe, from Portugal into Spain, etc., but the evidence concerning 

 this is as yet imperfect. In America, according to Logan, Dana, etc., 

 the principal parts raised at this time were the Green Mountain 

 regions, and the ridge extending from Lake Erie over Cincinnati into 

 Tennessee. These American ridges appear to have been raised to a 

 great height, and to have remained afterwards in part dry land, 

 even to the close of the Palseozoic. The islands in Europe were 

 raised only to a small height above water-level, and were probably 

 all again submerged by the close of the Upper Silurian. The up- 

 lifting did not take place in Britain until after the close of the Bala 

 period, or after the Upper Bala Limestone had been formed over the 

 British area. The changes may be said, therefore, to have taken 

 place when the Lower Llandovery rocks were beiug deposited over 

 the parts still submerged. The uplifting in Europe occurred chiefly 

 in regions where volcanic action had previously taken place, and the 

 changes seem to have been produced on the whole rapidly. For 

 instance, in Wales the upheaval, and a subsequent depression of most 

 of the upheaved parts, must have taken place during the time that the 

 Lower Llandovery rocks were being deposited in the surrounding 

 sea, for in many places the Upper Llandovery rocks may be now seen. 

 resting on the upturned edges of the Lower Silurian beds. Again, 

 as the Lower Llandovery rocks appear to have been made up for the 

 most part from the denudation of these islands, where an abundance 



