'Personal and Scientific News. 261 
Gol. McMahon argues in reply to Mr. R. 0. Oldham, that the foliation 
of granite, as in the Himalayes, is due to pressure acting on the intruded 
granite before it had become completely solidified and not to the meta- 
morphism due to pressure exerted on a cooled and solid rock. 
Messrs. Cornish and Kendall, following out a suggestion of Sorby's, 
detail the results of a series of experiments by Avhich they have proved 
that shells composed of the aragonite form of carbonate of lime are much 
more easily dissolved by carbonic acid water than shells composed of 
calcite. They suspended two fossil shells Pecten ofercularis (calcite) and 
Pectemculus glycimeris (aragonite) in a solution of carbonic acid and found 
that the latter lost weight much more rapidly than the former. The ex- 
periment was continued until the aragonite shell literally fell to pieces. 
That this change was due to structure rather than to the nature of the 
minerals was shown by performing the experiment wWh. poxvdered c^z- 
spar and -^\\.\\. j>oxvdered shells, in neither of which cases was any differ- 
ence observed in the rate of solution. The structure of shells composed 
of aragonite is, they state, looser than that of shells composed of calcite. 
The authors concluded by pointing out how these facts may ac- 
count for the disappearance of fossils composed of aragonite from rocks 
in which shells composed of calcite still remain, and quote several inst- 
ances in support of this opinion. 
PERSONAL AND SCIENTIFIC NEWS. 
Mexico and the Pacific Slope. Prof. A. E. Foote of 
1223 Belmont Ave. Philadelphia, Pa,, who has recently re- 
turned from a nine months stay in Europe, where he spent 
much time in Cornwall and Hungary, will soon start for a third 
trip through Mexico and the Pacific states returning by way 
of the Rocky Mountain region. 
A knowledge of the SjDanish language and a considerable ex- 
perience in Mexican mines will render his trip especially ser- 
viceable to those desiring information of these regions. 
Prof. J. P. Lesley is engaged on a summary of the re- 
sults of the Second Geological Survey of Pennsylvania which 
it is hoped will appear in no very long time. Such a work is 
exceedingly desirable in order to bring within the reach of work- 
ing geologists the mass of material accumulated and at jDresent 
almost buried in the more than fifty volumes of which the pub- 
lications of this survey consist. The work will be handsomely 
illustrated, with engravings, by various processes, of the prin- 
cipal fossils discovered during the prosecution of the work, and 
will be received with pleasure by geologists. 
