ANOTHER POSSIBLE CAUSE OF THE GLACIAL EPOCH. 145 



epoch of the Pleistocene, in fact, that it may have begun in 

 the PKocene period, and that their present development is the 

 ultimate outcome of erosive action continued through a very 

 long lapse of time.* This is a view which commends itself 

 to the judgment, and may be readily accepted. Possibly " the 

 continental shelf" may be the result of Pliocene erosion ; and 

 the deeper shelf with its cross-cutting channels, that of the 

 Pleistocene epoch. A Pliocene erosion extending down to 

 .100 fathoms, or less, would not have been sufficient to cut off 

 the arm of the Equatorial current from the Gulf of Mexico 

 to the extent effected in the later Pleistocene epoch, but may 

 have done so to some extent. We must not forget that the 

 decrease of temperature due to the diversion of the Atlantic 

 stream from its course into the Caribbean and Mexican Gulfs 

 into the North Atlantic was a slow and gradual change com- 

 mencing towards the close of the Pliocene and attaining its 

 maximum effect in the succeeding epoch. 



In concluding his memoir Dr. Spencer observes that "this 

 study estabhshes the great mobility of the earth's crust, and 

 opens out many new problems in dynamic geology." I 

 propose to deal Avith one of the more evident problems 

 arising from this inquiry ; namely, the effect of the uprising 

 of the Antill^an continent on the temperature of the Gulf 

 Stream, and on the consequent climatic conditions of 

 Western Europe and the adjoining regions. 



Part II. — The Gulf Stream. 



During the uprising of the Antillgean continent, that branch 

 of the great equatorial current wliich now enters the 

 Caribbean Sea and passes on into the Gulf of Mexico must 

 have pursued a very different course from that of the present 

 day. Its passage into the Gulf was debarred by the coast 

 of high continental land, the direction of Avhich must have 

 caused the current to pass directly northwards into the 

 North Atlantic as shown on the accompanying map (Plate). 

 Such a change in direction would result in a difference 

 of temperature, and we shall endeavour to ascertain, with 

 some degree of accuracy, the amount of variation as com- 

 pared with that of the present day. 



* This, indeed, may be inferred from the language of Professor 

 Spencer himself, when he says that the changes reached " their culminating 

 point " in the Pleistocene period. 



