io 4 THE POPULAR SCIENCE MONTHLY. 



able to that now existing in northern Germany, justify geologists 

 in concluding that this era was one of long duration, and charac- 

 terized in Germany by climatic conditions apparently not less 

 temperate than those that now obtain. 



4. To this well-marked interglacial era succeeded a second 

 overflow of Scandinavian inland ice, confined to a region much 

 narrower than that covered by the first. Its boundaries are shown 

 not only by the geographical distribution of the youngest bowlder- 

 clay, but by the direction of rock-striae, the trend of erratics, and 

 the position of well-marked moraines. 



Concerning the ground-moraines of the Alpine lands of cen- 

 tral Europe, the only question that has recently given rise to 

 much discussion is the origin of the materials themselves. The 

 observations of able investigators appear to Prof. Geikie to 

 have demonstrated that these materials have been derived, in 

 chief measure, from the underlying rocks by the erosive action 

 of the ice that overflowed them. German geologists are not 

 agreed upon this much-debated question of glacier-erosion — a few 

 still maintaining that glaciers have little or no eroding power. 

 But where the evidences of erosion have been studied over a 

 wide region, from which the ice has completely disappeared, 

 rather than at the lower ends of existing glaciers, some of the 

 strongest opponents of glacier-erosion have been compelled to go 

 over to the other camp. As an example, Prof. Geikie quoted 

 Dr. Blaas, who, through his observations on the glacial forma- 

 tions of the Inn Valley, has recanted his former views and be- 

 come a formidable opponent of the very theory which he once 

 upheld. To his books and to memoirs by Penck, Bruckner, and 

 Bohn, and especially to the chapter on glacier-erosion by the last- 

 named author, Prof. Geikie refers those who may be anxious to 

 know the last word on this question. 



Observations by Drs. Bruckner and Penck have led to the 

 opinion that the loess is of interglacial age. Examining a wider 

 range of evidence, Prof. Geikie has little doubt that the loess be- 

 longs to no particular horizon, though it must be considered 

 strictly a Pleistocene accumulation. Concerning its mode of 

 formation he discussed the various theories advanced, and gave it 

 as his opinion — an opinion formed from what he has himself seen 

 of the loess in various parts of Germany, from reading, and from 

 conversation with those who have worked over loess-covered re- 

 gions — that it is for the most part of aqueous origin, formed in 

 the slack waters of the great rivers, and in the innumerable tem- 

 porary lakes which occupied or partly occupied many of the val- 

 leys and depressions of the land. Probably some may have been 

 derived from the denudation of bowlder-clay, some from " rain- 

 wash/' while much of the so-called Bergloess with its abundant 





