554 REPORT — 1889. 



the stony clays thicken out as they are followed from the mountainous and high- 

 lying tracts to the low ground. Thus they are of inconsiderable thickness in 

 Norway, the higher parts of Sweden, and in Finland, just as we find is the case 

 in Scotland, Northern England, Wales, and the hilly parts of Ireland. Traced 

 south from the uplands of Scandinavia and Finland, they gradually thicken out 

 as the low grounds are approached. Thus in Southern Sweden they reach a 

 thickness of 43 metres or thereabout, and of 80 metres in the northern parts of 

 Prussia, while over the wide low-lying regions to the south they attain a much 

 greater thickness — reaching in Holstein, Mecklenburg, Pomerania, and West 

 Prussia a depth of 120 to 140 metres, and still greater depths in Hanover, Mark 

 Brandenburg, and Saxony. In those regions, however, a considerable portion of 

 the ' diluvium ' consists, as we shall see presently, of water-formed beds. 



The geographical distribution of the aqueous deposits which are associated 

 with the stony clays is somewhat similar. They are very sparingly developed in 

 districts where the boulder-clays are thin. Thus they are either wanting, or only 

 occur sporadically in thin irregular beds, in the high grounds of Northern Europe 

 generally. Further south, however, they gradually acquire more importance until 

 in the peripheral regions of the drift-covered tracts the}' come to equal and 

 eventually to surpass the boulder-clays in prominence. These latter, in fact, at 

 last cease to appear, and the whole bulk of the ' diluvium ' along the southern 

 margin of the diift area appears to consist of aqueous accumulations alone. 



The explanations of these facts advanced by German geologists are quite in 

 accordance with the views which have long been held by glacialists elsewhere, 

 and have been tersely summed iip by Dr. Jentzsch.^ The northern regions, he 

 says, were the feeding-grounds of the inland ice. In those regions melting was at 

 a minimum, while the grinding action of the ice was most effective. Here, 

 therefore, erosion reached its maximum — ground-moraine or boulder-clay being 

 unable to accumulate to any thickness. Further south melting greatly increased, 

 while ground-moraine at the same time tended to accumulate — the conjoint action 

 of glacier-ice and sub-glacial water resulting in the complex drifts of the peripheral 

 area. In the disposition and appearance of the aqueous deposits of the ' diluvium ' 

 we have evidence of an extensive sub-glacial water-circulation — glacier-mills that 

 gave rise to 'giants' kettles' — chains of sub-glacial lakes in which fine clays 

 gathered — streams and rivers that flowed in tunnels under the ice, and whose 

 courses were paved with sand and gravel. Nowhere do German geologists find any 

 evidence of marine action. On the contrary, the dove- tailing and interosculation 

 of boulder-clay with aqueous deposits are explained by the relation of the ice to the 

 surface over which it flowed. Throughout the peripheral area it did not rest so 

 continuously upon the ground as was the case in the inner region of maximum 

 erosion. In many places it was tunnelled by rapid streams and rivers, and here 

 and there it arched over sub-glacial lakes, so that accumulation of ground-moraine 

 proceeded side by side with the formation of aqueous sediments. Much of that 

 ground-moraine is of the usual tough and hard-pressed character, but here and 

 there it is somewhat less coherent and even silt-like. Now a study of the ground- 

 moraines of modern glaciers affords us a reasonable explanation of such differences. 

 Dr. Briickner - has shown that in many places the ground-moraine of Alpine glaciers 

 is included in the bottom of the ice itself. The ground-moraine, he says, frequently 

 appears as an ice-stratum abundantly impregnated with silt and rock-fragments — 

 it is like a conglomerate or breccia which has ice for its binding material. When 

 this gromid-moraine melts out of the ice — no running water being present — it forms 

 a layer of unstratified silt or clay, with stones scattered irregularly through it. 

 Such being the case in modern glaciers, we can hardly doubt that over the peri- 

 pheral areas occupied by the old northern ice-sheet boulder-clay must frequently 

 have been accumulated in the same way. Nay, when the ground-moraine melted 

 out and dropped here and there into quietly- flowing water it might even acquire 

 in part a bedded character. 



' Jahrh. d. konigl. preuss. geologiscTien Landcsanstalt fur 1884, p. 438. 

 * Die Vergletscherung des Salzachgebietes, &c. : OeograpMschc Abhandlnng&n, 

 Tierausgegehen r. A. Penck, Band I., Heft 1. 



