REVIEWS. 735 



lead to this conclusion. If the fourth epoch of Professor Geikie be no more 

 than an episode, as terms are used in America, the recognition of its proper 

 measure of distinctness is still important. An episode may ultimately come 

 to possess a significance scarcely less than that of an epoch. Even if the 

 "district" glaciers represented but a very moderate re-advance of the 

 ice, this re-advance is worthy of differentiation since it helps to empha- 

 size the general fact of the complexity of the glacial period as a whole. 



When we come to the separation of the fifth from the fourth 

 glacial epoch, and of the sixth from the fifth, it must be confessed that 

 the evidence presented is very far from convincing, if the word epoch 

 is to retain the meaning which has been attached to it in this country. 

 From the written page it does not appear that the so-called fifth and 

 sixth glacial epochs of Scotland necessarily amount to more than con- 

 siderable recrudescences of glaciers which were previously retreating. 

 But even if these recrudescences be of minor extent only, they should 

 be recognized for what they are. If they be not separate epochs, in our 

 sense of the term, there can be no doubt that they represent more or 

 less distinct advances of the ice, and their separate recognition helps 

 to emphasize what seems to be the fact in America as well as in Europe, 

 viz., that the glacial period was long and complex. To this conclu- 

 sion detailed work on both continents seems to be surely leading. 



The drift of Southern England, "rubble drift," "head," etc., is 

 ascribed to torrents connected in time with the ice epoch. The material, 

 if we understand Professor Geikie rightly, is not for the most part mate- 

 rial that was worked over by the ice, but rather the product of rock 

 disintegration in cold climates. It is believed that the frozen surface 

 outside the ice prevented the penetration of the rain water. Under these 

 conditions, precipitation and drainage might give rise, especially in the 

 warmer seasons, to considerable floods. Such waters, it is believed, 

 bore the rubble from its native place and spread it upon the plains to 

 the south. If this interpretation be correct, it may have an important 

 bearing on gravel deposits outside the glacial drift in other countries. 



On the continent, "upper" and "lower" series of drift deposits are 

 recognized on all hands. There are numerous beds which have been 

 more or less generally classed &S interglacial. They are found at inter- 

 vals over a stretch of country extending from the North Sea to Mos- 

 cow. Many of the continental geologists have been in the habit of 

 putting them together, and of regarding them as the great division 

 plane between the "upper" and "lower" tills. Independently of the inter- 



