1905-6.] Is BELIEF IN A GLACIAL PERIOD JUSTIFIED? 287 
(and might not corresponding depressions produce the same) bodies of 
water have the power of hurling on enormous blocks, sand and gravel to 
vast distances and over considerable inequalities, we are relieved from 
one of the great difficulties opposed to the rational explanation of the 
position of a very large proportion of this drifted material. Whatever 
may have been the period of their action, such aqueous débacles, have 
probably formed many of the conglomerates of previous ages and with 
the help of ice floes, much of that foreign drift, of which we have already 
treated.”’ 
Prof. Tyndall says, ‘‘the creation of a glacier, or a glacial period is 
really a process of distillation on a great scale, in which a sufficient supply 
of vapour in the air, is quite as important a factor, as a sufficiently power- 
ful condenser to convert it into snow and ice, and the process of making 
vapour and condensing it, must be going on at the same time in different 
areas. We cannot condense the vapour made in summer, by the winter’s 
cold, because we cannot store up that vapour. Vapour is lighter than air 
and air charged with vapour immediately rises, until it reaches a higher 
altitude, there it finds greater cold and inevitably discharges its moisture, 
generally in the shape of rain. This causes the great rainfall in the tropics. 
In the supposed case, therefore, of a hotter if shorter summer, would no 
doubt evaporate more water per day, but vapour thus made would descend 
in the shape of rain long before the winter came, and when it came there 
would undoubtedly be greater cold to condense what vapour there was. 
So that the amount of vapour left in the air would be very slightly, if any 
more, with great eccentricity than with a small one and there would have 
been little or no appreciable effect on the snowfall.’”’ Recurrent glaciation 
should show traces in the earlier formations, but James Geikie says, 
“We look in vain for Cambro-Silurian rochés moutonnées and boulder 
clay or moraines.’’ The same may also be said of all the succeeding 
formations in the Paleozoic and Mesozic, besides there are many indica- 
tions of considerable heat, that would preclude the possibility of any gla- 
ciation during those epochs. 
Prof. Andrews speaking of the gravel deposits of the United States, 
says, ‘‘These gravel hills are often sharp and conical and interspersed with 
deep valleys without outlets (potash kettles). ... . It would seem an 
unavoidable inference, that our drift of this region, not only came from 
the north, but it came in a vast sweep of water, deep enough to cover 
gravel hills 800 feet high and with velocity enough to throw such coarse 
material into lofty and steep summits.’ T. Bergmann so far back as 1769, 
noted similar phenomena in Sweden, which he calls (Giants, Cauldrons). 
He claims they are ‘‘due to the working of stones arrested by some im- 
pediment and then made to turn round by water.’’ He quotes one which 
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