Editorial Comment. 247 
Prof, H. Credner: The occurrence of the sand between two ground- 
moraines indicates a retreat and second advance of the ice sheet. Such 
interpolated sands are in Germany always local and no proof of a real 
iuterglacial epoch. The sand layers between the moraines are not con- 
tinuous, but local, and cannot be given the significance attributed to 
them by Wahnschaife. 
Prof. Pavlow: In order to secure a satisfactory classification of Qua- 
ternary deposits, we must secure a satisfactory definition of Pleistocene. 
Prof. Pavlow said he would like to give his own views, but would post- 
pone them until such accepted definition had been arrived at. 
Baron de Geer agreed with Wahnschaffe that the chronolog ical class- 
ification is at least locally possible. He also recognized two glacial 
•epochs, due to two great oscillations. These cannot always be separated, 
as, for instance^ in Russia. For this reason it is best to commence 
with a genetic classification, since this causes less confusion to the field 
geologist. 
Dr. WahnschafEe replied to Prof. Credner's assertion that there is no 
proof of an interglacial period in northern Germany. He thought that 
the existence of a diluvial fauna between the two tills is suflicient proof. 
Prof. Credner replied that no complete skeleton had been found, but 
onlj' single bones which might have been transported and deposited with 
the gravel. 
Dr. Wahnschaffe again replied that the bones occurring in these 
gravels are proportionately large, when compared with the gravels them- 
selves, and therefore cannot well have been transported from a distance. 
Prof. Shaler: Organic deposits mav possibly occur very near the ice 
sheet, which allows an interweaving of organic and glacial deposits. 
Mr. G. K. Gilbert remarked on the observation of I. C. Russell in 
Alaska, that where the movement of the ice is verj^ sluggish, it may 
become covered with soil, or even with a growing forest, in which such 
animals as bears still live. 
Dr. Diener remarked that intercalated beds of sand were no positive 
proof of interglacial periods. In the Austrian Alps moraines no more 
than twenty years old are covered with pasture, and in the Caucasus the 
rhododendron grows to the very edge of the ice. 
Dr. Hoist mentioned two moraines separated by interpolated sand and 
thought that they might both have l)een formed by the same ice sheet. 
The melting of the ice leaves an uno.\:idized(blue) ground-moraine, with 
an overlying oxidized (j'ellow) upper moraine. This occurs in northern 
Sweden where there is no indication of a retreat of the ice. 
Baron de Geer could not understand the occurrence of thirty or forty 
feet of stratified sand l)etweea two moraines of the same glacier. The 
colors are sometimes the reverse of what has been stated by Dr. Hoist, 
and the boulders in the two moraines have been derived from different 
sources. 
Mr. Christie described the section of peat and silt between two layers 
■of till, occurring on the river Clyde, above Glasgow. 
Mr. Cadell described some five distinct layers of till occurring in a 
