GEOLOGY AND MINERALOGY. 469 
t 
latter substance is found to be a hydrated silicate of alumina, protoxide 
of iron, magnesia, and potash: the alumina thus replacing, in great 
part, the oxide of iron of the green grains so abundant in many 
. Cretaceous deposits. Mr. Hunt’s Report concludes with a long and 
very elaborate review of the formation of magnesian limestones, in 
continuation of his previous communications on that subject. The 
results of various ingenious experiments, involving numerous analyses 
and a great amount of patient research, are given in connexion with 
this enquiry, one of the most important perhaps, undertaken of late 
years, in the department of Chemical Geology. As it is impossible to 
do justice to these contributions by mere extracts, we have inserted 
one of them in an entire form, in another part of the journal. The 
one selected is the first alluded to above, a paper of much value, on 
the trachytic and other eruptive compounds of Montreal and the 
adjoinmg metamorphic district south of the St. Lawrence. Apart 
from the interest attached to these rocks as remarkable examples of 
eruptive products occurring on Canadian soil, Mr. Hunt’s investigation 
of their characters and composition tends greatly to clear up the 
obscurity which still prevails respecting the true relations and subdi- 
visions of the intrusive rocks generally. 
E, J, C. 
SCIENTIFIC AND LITERARY NOTES. 
GEOLOGY AND MINERALOGY. 
ADDITIONAL FOSSIL TRACKS IN THE POTSDAM SANDSTONE OF CANADA, 
The celebrated fossil foot-tracks of Beauharnois, Vaudreuil, and other neighbour- 
ing localities, constitute, it is well known, one of the most remarkable character- 
istics of our Potsdam formation. They have been referred by Professor Owen, 
under the generic name of Protichnites, to an unknown crustacean of which no 
other traces have been met with. During the course of last year, Dr. James 
Wilson of Perth (Canada West), discovered in some quarries of Potsdam Sandstone, 
in the vicinity of that town, some still more remarkable impressions, These, 
which are associated with the tracks of Protichnites, have been recently figured 
and described in full, in the Canadian Naturalist, by Sir W. E. Logan. They 
consist, to quote from Sir William Logan’s description, “ of a number of parallel 
ridges and furrows something like ripple marks, which are arranged (transversely) 
_ between two narrow continuous parallel ridges, giving to the whole impression a 
form very like that of a ladder, and, as the whole form is usually gently sinuous 
