ON THE PROGRESS OF GEOLOGY. AOI 
signs of the glacial period by the oscillation of the sea-level. 
Penck’s views in this respect are different from those of Adhemar 
and Croll. 
Another factor for explaining great changes on the Earth’s 
surface, brought about in geological periods long past, has lately 
been put forward under the name of Tidal Evolution, a very in- 
genious theory, first worked out in its entirety by G. H. Darwin. 
It is based upon the action of the moon, once a part of our 
planet, on the earth, producing the tides and retarding its motion, 
as well as upon the reaction of the earth upon its satellite. 
Gradually the moon was driven away from our planet, and the 
length of day has thus at the same rate become more consider- 
able. 
However, when Professor Robert Ball, in Dublin, and others 
attempt to make out that the former much larger tides, when the 
moon was closer to the earth, formed a powerful agent for the 
destruction of rocks existing at that time, and for the formation 
of newer beds from them, by which the thickness of the older 
sedimentary and fossiliferous strata can be explained, I think 
we have to pause before we can accept such a sequence. 
Moreover, according to Sir William Thomson, there has 
not been any great change in the ellipticity of the earth’s 
figure since its consolidation, consequently Mr. Darwin’s views 
as to higher tides have to be modified, as he presupposes a more 
considerable ellipticity for his calculations. However, even 
assuming Professor Ball’s calculation that when the moon was 
only 40,000 miles distant from the earth, the tides at that time 
would rise and fall between 600 to 700 feet twice in 24 hours, 
to be correct, I have no doubt that it was long before the Cam- 
brian or lowest fossiliferous rocks with which we are acquainted 
were deposited. The occurence of numerous fossils in the oldest 
beds, belonging to animals that could live only in clear water, 
and minute ripple marks on the rocks, speak clearly against 
Professor Ball’s hypothesis. 
This speculation in Physical Geology has already been 
tested by various geologists to account for the so-called Marine 
Denudation. This expression was first introduced by Sir 
Andrew Ramsay for the higher portions of ridges over large 
areas, that if laid down on an imaginary plane, appear to have 
once formed one surface with a very gradual slope in one direc- 
tion. 
However, this peculiar appearance can, as I have repeatedly 
suggested in former publications, be easily explained by the fact, 
that when the land gradually rose above the sea-level, abrasion 
on a gigantic scale must have taken place, by which, in the case 
of our Southern Alps, the whole had the appearance of a shallow 
dome, of which the western side was much steeper than the eastern, 
till the subzerial erosion by atmospheric agencies or, as I called 
t, ridge-making, took place. 
Before leaving this subject, to which I have devoted more 
time than perhaps I ought to have done, I may add that many 
