TKAXSACTIONS OF SECTION C. 553 



trary, the character of the morainic accumulations, and the symmetrical grouping 

 and radiation of the erratics and perched blocks over the foot-hills and low grounds, 

 show that these last have been invaded and overHowed by the glaciers themselves. 

 Even the most strenuous upholders of the efficacy of icebergs as originators of 

 some boulder-clays admit that the boulder-clay or till, of what we may caU the 

 inner or central region of a glaciated tract, is the product of land-ice. IJnder this 

 category comes the boulder-clay of Norway, Sweden, and Finland, and of the 

 Alpine lands of Central Europe, not to speak of the hilly parts of our own islands. 



When wo come to study the drifts of the peripheral areas it is not diihcult to 

 see why these should be considered to have had a diflerent origin. They present 

 certain features which, although not absent from the glacial deposits of the inner 

 region, are not nearly so characteristic of such upland tracts. I refer especially to 

 the frequent interstratification of boulder-clays with well-bedded deposits of clay, 

 sand, and gravel ; and to the fact that these boulder-clajs are often less compressed 

 than those of the inner region, and have even occasionally a somewhat silt-like 

 character. Such appearances do seem at first to be readily explained on the assump- 

 tion that the deposits have been accumulated in water opposite the margin of a 

 continental glacier or ice-.sheet — and this was the view which several able investi- 

 gators in Germany were for some time inclined to adopt. 



But when the phenomena came to be studied in greater detail, and over a 

 wider area, this preliminarj' hypothesis did not prove satisfactory. It was dis- 

 covered, for example, that ' giants' kettles ' ' were more or less commonly dis- 

 tributed under the glacial deposits, and such ' kettles' could only have originated 

 at the bottom of a glacier. Again, it was found that preglacial accumulations 

 were plentifully developed in certain places below the drift, and were often 

 involved with the latter in a remarkable way. The ' brown-coal-formation ' in 

 like manner was violently disturbed and displaced, to such a degree that frequently 

 the boulder-clay is found to underlie it. Similar phenomena were encountered 

 in regions where the drift overlies the Chalk, the latter presenting the appear- 

 ance of having been smashed and shattered — the fragments having often been 

 dragged some distance, so as to form a kind of friction-breccia underlying the 

 drift, while large masses are often included in the clay itself All the facts 

 pointed to the conclusion that these disturbances were due to tangential thrusting 

 or crushing, and were not the result of vertical displacements, such as are produced 

 by normal faulting, for the disturbances in question die out from above down- 

 wards. Evidence of similar thrusting or crushing is seen in the remarkable faults 

 and contortions that so often characterise the clays and sands that occur in the 

 boulder-clay itself. The only agent that could produce the appearances now 

 briefly referred to is land-ice, and we must therefore agree with German geologists 

 that glacier-ice has overflowed all the drift-covered regions of the peripheral area. 

 No evidence of marine action in the formation of the stony clays is forthcoming — 

 not a trace of any sea-heach has been detected. And yet, if these clays had been 

 laid down in the sea during the retreat of the ice-sheet "from Germany, surely such 

 evidence as I have indicated ought to be met with. To the best of my knowledge 

 the only particular facts which have been appealed to, as proofs of marine action, 

 are the appearance of bedded deposits in the boulder-clays, and the occasional 

 occurrence in the clays themselves of a sea-shell. But other organic remains are 

 also met with now and again in similar positions, such as mammalian bones and 

 fresh-water shells. All these, however, have been shown to be derivative in their 

 origin— they are just as much erratics as the stones and boulders with which they 

 are associated. The only phenomena, therefore, that the glacialist has to account 

 for are the bedded deposits which occur so I'requently in the boulder-clays of the 

 peripheral regions, and the occasional silty and uncompressed character of the 

 cla\s them.«elves. 



The iutercaLited beds are, after all, not hard to explain. If we consider for a 

 moment the geographical distribution of the boulder-clays, and their associated 

 aqueous deposits, we shall find a clue to their origin. Speaking in general terms 



' These appear to have been first detected by Professor Bercndt and Professor E. 

 Geinitz. 



