ANOTHER POSSEBLE CAUSE OP THE GLACIAL EPOCH, 167 



movements of the land on alternate sides of the American con- 

 tinent the recent paper by Professor J. W. Spencer on " Great 

 Changes of Level in Mexico and the Interoceanic Connections" 

 (referred to above), have thrown much light. 



The observations of Professor Gresley on the American " clay- 

 veins " of the Pennsylvanian coal measures, an account of which I 

 recollect reading some time ago, show how physical phenomena, 

 apparently widely disconnected, may really have a bearing on each 

 other. I have been much interested by the views of the Rev. R. A. 

 BuUen, in which I fully concur, and am glad to have the support 

 of an observer who has paid so much attention to the physical 

 conditions of the North Atlantic. 



The observations of Cav. W. P. Jervis are of much interest 

 and very gratifying. I have had several letters of acknowledg- 

 ment expressing interest in the subject of my paper from conti- 

 nental geologists, including Professor Dames, of Berlin, Dr. C. 

 Barrois, of Lille, Professor Suess, of Vienna, and Professor 

 Geinitz, of Dresden, and this of Cav. Jervis, of Turin, is a 

 welcome addition to the list. The statement that Issel has 

 traced old river courses to great depths in the Mediterranean in 

 prolongation of valleys in North Italy is new to me, and is quite 

 confirmatory of the results arrived at by the late Admiral Spratt, 

 where he proved by soundings the existence of a river channel 

 joining two of the lakes formed in the Mediterranean basin 

 between Sicily and Africa du.ring the period of upheaval and low 

 water-level. (See Quart. Jour. Geol. Soc, Lond., vol. xxiii, p. 

 292.) The existence of this channel shows the bed of the 

 Mediterranean to have been upraised over 150 fathoms (900-1,000 

 feet) at this period. 



As regards the points which the writer suggests in reference to 

 the conditions of the Atlantic previous to the formation of the 

 Gulf Stream, 1 hope to be able to give them attention. 



