362 G. F. Wright — Unity of the Glacial Epoch. 



From the discussions in the International Congress of Geol- 

 ogists at Washington in 1891, it would appear also that a fair 

 share of the European members did not regard the interstrati- 

 fied gravel deposits of North Germany as indicative of any- 

 thing more than a temporary oscillation of the ice. (See Am. 

 Geo!.. Oct., 1891, pp. 211 to 217.) The " interglacial shell 

 beds" at elevations of 1,000 and 1,400 feet above sea in 

 England at Macclesfield and Moel Tryfaen, have been shown 

 to be shells pushed up from the Irish Sea, and washed out and 

 stratified in thin beds by the local streams of water accom- 

 panying the departure of the ice sheet. (See my paper in 

 this Journal, Jan. 1892 ; but especially Professor Kendall's 

 comprehensive discussion of the evidence in my volume just 

 published by D. Appleton & Co., entitled Man and the Glacial 

 Period, pp. 136-182.) Professor Lewis's conjecture seems to 

 be amply sustained by subsequent investigations. The evi- 

 dence for a succession of glacial periods in Great Britain is 

 inconclusive, while the evidence against it is overwhelming. 

 Professor James Geikie has indeed recently returned to the 

 defence of his favorite theory (see On The Glacial Period 

 and the Earth Movement Hypothesis, being a paper read 

 before the Yietoria Institute, London), in which he relies 

 almost wholly upon evidence of successive glacial periods to 

 prove that the astronomical theory, to which we have referred, 

 is the only adequate cause. His evidence is largely drawn 

 from interglacial beds on the continent of Europe containing 

 remains of plants and animals. The strongest instance ad- 

 duced by him is still that of the interglacial lignite beds of 

 Diirnten and Utznach in Switzerland. But it would seem 

 that the inference of great oscillations of climate which he 

 draws from the character of the vegetation composing the 

 lignites rests upon very uncertain data. The remarks of Pro- 

 fessor Prestwich upon the deposits are of great weight : 



" Admitting the fact that the Diirnten Lignites rest on beds 

 of undoubted glacial (ground moraine) origin, and that the 

 trees grew on the spot where their stumps and remains are 

 found, it by no means follows, as contended, that because 

 these trees are all of species now living in Switzerland that 

 the temperature was as high as that of Switzerland at the 

 present day. The Pinus sylvestris, Abies excelsa, the Yew, 

 the Birch, and the Oak, flourish equally in Sweden and far 

 north in Siberia, and there is an absence in the scanty Diirnten 

 flora of those plants which, while having a more southern 

 range, also now live in Switzerland. On the other hand, there 

 is there one species of Pinus (P. Montana) which is spread 

 over the mountain country up to heights of 7,000 feet, and is 

 rare in the lowlands, while one of the mosses in the lignite is 



