ANNIVERSARY ADDRESS OF THE PRESIDENT. Ixix 



on the mountains than occurs at present *, and would thus furnish 

 an additional quota to the bulk of the glaciers. 



Tt was under these conditions, with glaciers creeping forth from 

 all the deep valleys, either into the waters or over the surface of 

 ice which coated the lake during a long winter, that erratic frag- 

 ments of the older rocks, entangled in or supported upon icebergs 

 and floes, were drifted across to the opposite shores, and there 

 formed the long lines of grave) s and boulders, and effected the 

 scoring and polishing of the rocks, for which the long range of the 

 Jura has attracted in so great a degree the attention of observers. 



The Swiss geologists, and among them Professor Heer, look upon 

 it as probable that there have been two Glacial periods — one before 

 and the other after the deposition of the brown coals of Wetzikon, 

 Utznach, &c. This alternation of conditions may be explained by 

 oscillations of level, such as have been observed and inferred for 

 other districts and other formations ; but, if considered indepen- 

 dently of the amount of elevation of the land, it would need the hypo- 

 thesis of a twice-repeated decrease and increase of the mean annual 

 temperature by above 12|° F. — an irregularity inconsistent with the 

 theory of terrestrial heat. 



When at length the final depression of the district began to take 

 place, Waltershausen shows grounds for inferring that it was by 

 very slow degrees, and with unequal progress of subsidence, whence 

 he agrees with Studer that the present lakes mark the tracts in 

 which the variableness of the movement produced the deepest hollows, 

 and argues that the stone-heaps (Steindamme) which border the 

 lower end of so many of the Swiss lakes, are not actual moraines, 

 but consist of the drifted blocks and debris transported by the later 

 action of floating ice-masses, when the upland lake had, in the course 

 of constant depression, been reduced to within these narrow limits. 



Turning to the south side of the Alps, it is shown that a long 

 marine gulf extended from Venice and Chioggia to the foot of the 

 maritime Alps, from which a number of long inlets, or fiords, ex- 

 tended northward when the elevation of the Alps commenced. If 

 it be sought to explain the former great extension of the glaciers 

 along the valleys on this side of the chain without having recourse 

 to a general elevation of land, we must introduce the supposition of 

 a decrease of the annual mean temperature by about 10° C. (18° F.), 

 an amount which cannot be expained either by a succession of cold 

 years, on Charpentier's hypothesis, or by a diff'erent distribution of 

 land and sea. But if an elevation to the amount of about 4000 feet 

 be assumed to have occurred, the phenomena will be accounted for, 

 as on the north side of the chain ; and the subsequent gradual de- 

 pression will have broken up still further into isolated basins that 

 district of lakes, many of them formerly in communication with each 

 other, which may be regarded as the remnant of the ancient Lom- 

 bardo-Yenetian gulf. 



I must not attempt to follow out the numerous facts observed in 



* The exceptional exceeds the average rainfall of the present day in Switzer- 

 and by about 10 per cent. 



