462 Reports and Proceedings—British Association— 
that hypothesis has never been able to survive a moderate amount 
of accurate observation. Hven in Switzerland—the land of glaciers 
—geologists at one time were of opinicen that the Boulder-clays of 
the low grounds had a different origin from those which occur in 
the mountain-valleys. Thus it was supposed that at the close of the 
Pleistocene period the Alps were surrounded by great lakes or gulfs 
of some inland sea, into which the glaciers of the high valleys 
flowed and calved their icebergs—these latter scattering erratics and 
earthy débris over the drowned areas. Sartorius von Waltershausen ! 
set forth this view in an elaborate and well-illustrated paper. Un- 
fortunately for his hypothesis, no trace of the supposed great lakes 
or inland sea has ever been detected—on the contrary, the character 
of the morainic accumulations, and the symmetrical grouping and 
radiation of the erratics and perched blocks over the tfoot-hills and 
low grounds, show that these last have been invaded and overflowed 
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 call the inner or central 
region of a glaciated tract, is the product of land-ice. Under 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 we come to study the drifts of the peripheral areas it is not 
difficult to see why these should be considered to have had a different 
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-clays 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 assumption 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 investigators 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 preliminary hypothesis did not prove 
satisfactory. It was discovered, for example, that ‘ giants’ kettles”? 
were more or less commonly distributed under the glacial deposits, 
and such “kettles” could only have originated at the bottom of a 
glacier. Again it was found that pre-Glacial 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 
1 Untersuchungen tiber die Klimate der Gegenwart und der Vorwelt, etc. 
Natuurkundige Verhandelingen vy. d. Holland, Maatsch. d. Wetensch. te Haarlem, 
1866 
2 These appear to have been first detected by Professor Berendt and Professor 
E. Geinitz. 
