The Scottish Naturalist. 199 



and before these had become confluent with the glacier of the 

 Isere, &c, the secondary mountain-ranges of Savoy and Dau- 

 phiny and the hills of Bugey were covered with very consider- 

 able snow-fields, from which local glaciers descended all the 

 valleys to the low ground. But when the vast ice-flows of 

 Switzerland, Upper Savoy, &c, at last became confluent, they 

 completely overflowed many of the hilly districts which had 

 formerly supported independent snow-fields and glaciers, and 

 deposited their bottom-moraines over the morainic debris of 

 the local glaciers. In other cases, where the secondary hill- 

 ranges were too lofty to be completely drowned in the great mer 

 de glace, long tongues of ice dilated into the valleys, and com- 

 pelled the local ice out of its course ; sometimes, as in the case 

 of the Valromey, forcing it backwards up the valleys down 

 which it formerly flowed. But when once more the mighty 

 mer de glace was on the wane, then the local glaciers came again 

 into existence, and reoccupied their old courses. And thus it 

 is that in the hilly regions at the base of the higher Alps, and 

 even out upon the low grounds and plains, we encounter that 

 remarkable commingling of erratics which has been described 

 above. Not unfrequently, indeed, we find one set of moraines 

 superposed upon another, just as in the low grounds of North- 

 ern Germany, &c, we may observe one boulder-clay overlying 

 another, the erratics in which give evidence of transport in 

 different directions. The observations recorded by MM. 

 Falsan and Chantre, and their colleagues, thus demonstrate 

 that " intercrossings " of erratics of the most pronounced 

 character have been brought about solely by the action of 

 glaciers. In the case of the erratics and morainic accumula- 

 tions of the basin of the Rhone, the action of icebergs is 

 entirely precluded. 



I may now mention some of the more remarkable examples 

 of " intercrossings " of erratics which have been recorded from 

 the glacial accumulations of North Germany, &c. An exami- 

 nation of the glacial striae, roches mouto.nnees, and boulder-clays of 

 Saxony leads to the conviction, according to Credner, Penck, 

 Torell, Helland, and others, that the whole of that region has 

 been invaded by the great Scandinavian mer de glace which 

 flowed into Saxony from N.N. E. to S.S.W. Erratics from 

 Southern Sweden and Gothland occur in the boulder-clay, and 

 the presence of these, taken in connection with the direction of 

 the glaciation, leaves us no alternative but to agree with the 



