fe. 
Correspondence—Mr. W. Topiley. 573 
in the last three years. During the past year the boulder has been 
at a part of the glacier which is steeper than where it was previously. 
This may explain the slightly accelerated movement during the last 
year. Ido not rely implicitly on the 44 days’ observation, but if 
it be assumed to be correct, it leads to the inference that the move- 
ment in summer is 2 in. per day, and in winter 1 in. 
In the first four years there was no perceptible disturbance of the 
position of the boulder on the sustaining ice. During the last year 
it has twisted a little. 
Last summer I took some observations to ascertain the superficial 
waste of the glacier on a part which was free from moraine (during 
fine sunny weather), and found it amount to about 3in. per day. 
This summer I have again taken observations, in a different manner, 
extending over 21 days; these gave a result of over 2in. per day. 
Forbes states that the waste is as much as 3in. a day in a hot 
summer. Now on comparing the scale of movement with that of 
the waste by melting, I get results which I cannot reconcile. 
The boulder which I have had under observation cannot have 
come from any mountain which is less than three miles distant 
from its present position. The angle of the glacier above the part 
where it rests, is less, rather than greater. I therefore assume that 
the recorded rate of movement may be taken as an average, in 
which case the boulder must have been travelling 400 years. 
The depth of the glacier is probably not more than 300 feet, but 
I will assume it to be 600 feet, and that the average waste is only 
two inches a day, during three summer months, or fifteen feet per 
annum. On this assumption the whole depth of 600 feet would be 
melted in forty years. I have taken observations of the relative 
movement of the glacier, where covered with moraine, and also 
where free from it. They do not encourage the supposition that 
there is any material difference. F. Luoyp. 
19th August, 1880. 
THE PERMANENCE OF OCEANS AND CONTINENTS. 
Str,—Mr. T. M. Reade, in your September Number, quotes certain 
authors who believe that oceans and continents have, throughout all 
known geological time, occupied pretty much the same relative 
positions as now. 
There is, however, one important omission in this list. In the 
famous chapter in the Origin of Species, “On the Imperfection of 
the Geological Record,” Mr. Darwin endeavours to account for the 
sudden appearance of groups of allied species in the lowest known 
fossiliferous strata; he does this by assuming that the Pre-Silurian 
continents probably existed where the oceans now are. He says: 
“We may infer that where our oceans now extend, oceans have 
extended from the remotest period of which we have any record; 
and on the other hand, that where continents now exist, large tracts 
of land have existed, subjected no doubt to great oscillations of 
level, since the earliest Silurian period. ..... At a period im- 
measurably antecedent to the Silurian epoch, continents may have 
