226 PROFESSOR JAMES GEIKIE, LL.B., D.C.L., F.R.S., ETC., ON 



" coral sand," with bryozoa. The flora and fauna have a 

 distinctly temperate facies. It is no wonder, then, that 

 continental geologists are generally inclined to admit that 

 North Germany and the contiguous countries have been 

 invaded at least twice by the ice-sheets of two separate and 

 distinct glacial epochs. This is not all, however. While 

 every observer acknowledges that the " diluvium " is properly 

 divided into an upper and a lower series, there are some 

 geologists who have described the occurrence of three, and 

 even more boulder- clays — the one clearly differentiated from 

 the other, and traceable over wide areas. Is each of these 

 to be considered the product of an independent ice-sheet, or 

 do they only indicate more or less extensive oscillations of 

 the ice-front % The boulder-clays are parted from each other 

 by thick beds of sand and clay, in some of which fossils have 

 occasionally been detected. It is quite possible that such 

 stratified beds were deposited during a temporary retreat of 

 the ice-front, which when it re-advanced covered them up 

 with its bottom-moraine. On the other hand, the phenomena 

 are equally explicable on the assumption that each boulder- 

 clay represents a separate epoch of glaciation. Until the 

 stratified beds have yielded more abundant traces of the 

 life of the period, our judgment as to the conditions implied 

 by them must be suspended. It is worthy of note in this 

 connection, however, that in North America the existence of 

 one prolonged inter glacial epoch has been well established, 

 while distinct evidence is forthcoming of what Chamberlin 

 terms " stages of deglaciation and re-advancing ice."* 



When we turn to the Alpine lands, we find that there also 

 the occurrence of former interglacial conditions has been 

 recognised. The interglacial deposits, as described by Heer 

 and others, are well known. These form as definite a geo- 

 logical horizon as the similar fossiliferous zone in the 

 " diluvium " of Northern Germany. The lignites, as Heer 

 pointed out, represent a long period of time, and this is still 

 further illustrated by the fact that considerable fluviatile 

 erosion supervened between the close of the first, and the 

 advent of the later glacial epoch. No mere temporary 

 retreat and re-advance of the ice will account for the 

 phenomena. Let us for a moment consider the conditions 

 under which the accumulations in question were laid down. 



* Sixth Annual Report, U.S. Geol. Survey, 1884-85, p. 315. 



