368 CLIMATIC COXDITIOXS OF THE GLACIAL EPOCH. 



it is almost a century since Wrede promulgated the idea that the boulders of 

 Northern Germany had been brought there by icebergs,* it is only within a 

 few years that geologists have begun to make minute explorations in regard 

 to the position of the localities from whicli the materials in question have 

 been brouiiht. 



The diluvium — the name by which the superficial detrital materials, not 

 alluvial, are generally called by the German geologists — of North Germany 

 is always well water-worn. It consists of sand, gravel, mai'l, marly clay — 

 in short, of rolled fragmental and connninuted material of all sizes. In some 

 localities there are even beds of imperfect coal [Braunkohle] enclosed in it. 

 Much of this material is stratified ; in some cases it is verj^ irregularly heaped 

 together. 



To the east of the Weser this detritus is largely of northern origin ; west 

 of that river this is much less the case, and as we go south on the great 

 German plain, we find more and more material of southern origin mixed 

 with it. Between the Saal and the Oder southern detritus is largely inter- 

 mingled with that of northern origin, and in places exceeds it in quantity. 

 Near Leipsic the gravel is chiefly made up of southern materials.f But to 

 give even the briefest abstract of what has been done in this line of in- 

 vestigation would require more space than is here at the writer's command. 



As a specimen, however, of what is doing towards a solution of some of 

 the problems connected with the origin and distribution of the superficial 

 detritus of this region, the investigations of Professor Martin of Leyden may 

 be mentioned, and some of his principal results cited. This geologist has 

 examined with care the erratics of Holland, and particularly those of sedi- 

 mentary fossiliferous rock, for the purpose of referring them so fiir as possible 

 to the region from which they were brought. It is a curious fact that these 

 deposits of foreign boulders, all of which are thoroughly rolled and water- 

 worn, are not spread rather uniformly' over the country, as is chiefly the case 

 to the east of the Elbe, but collected in certain localities in large quantity 

 [an einzelnen Punkten in grossen Mengen aufgehaiift], Avhile the interven- 

 ing ground is almost entirely free from them. These rolled rock-fragments 

 represent various geological formations. Those of Silurian age are predomi- 

 nant, and are found on examination to have come from the Baltic Provinces, 



* In Geologisclie Rcsultate aus Beobaclitungen iiber eiuen Tlieil der Siidbaltischen Lander, Berlin, 1794- 

 + These statements are chiefly on the authority of Jentzsch in Schriften der phys.-cekonoiii. Gesellsehaft zu 

 Konigsberg, 1877, p. 228, and Dathe in Neues Jahrbucli fiir Mineralogic, 1877, p. 165. 



