ANNIVERSARY ADDRESS OF THE PRESIDENT, Xcix 
crushing and grinding of ice-floes on the coasts, as they are to be 
found detailed in our voyages to the northern regions of America, 
are points of importance not to be neglected when we take a general 
view of the phenomena connected with erratic blocks. Indeed there 
are cases in our own land where this explanation would accord best 
with the facts observed. 
In a notice on the Heights of the Jura between the Dole and Re- 
culet, M. Jules Marcou gives a detailed account of that portion of 
the Jura range in which its chief heights are included. He observes 
that the four groups of Jurassic rocks are not exposed on these 
heights, the upper and Oxfordian divisions being alone visible, whilst 
the two lower groups occur more eastward in the lower range of the 
department of the Ain. The lower part and the great valleys of the 
Dole and the Reculet are composed of neocomian rocks, and the 
author infers that when the latter were deposited the mass of these 
mountains and of Mont-Crédoz formed an island bathed by the sea, 
im which the neocomian deposits were effected. M. Marcou points 
out, that while the Oxfordian group, surrounding the ancient Hercy- 
nian and Vosgian islands, is characterized by a considerable develop- 
ment of marls, containing numerous pyritous fossils, the same group 
of the Jura is formed of a great thickness of greyish-blue limestones, 
more or less compact and marly. This difference of lithological 
structure the author attributes to the more littoral character of the 
Hereynian and Vosgian deposits, and the more pelagic conditions 
under which the accumulations of the Jura were effected at the same 
date. After pointing out these changes, M. Marcou states that the 
palzeontological character of the deposits corresponds with their litho- 
logical. Thus in the littoral regions the species are numerous, and. 
more especially belong to the cephalopods, the gasteropods and ace- 
phala; in the subpelagic regions the individuals have much dimi- 
nished, the cephalopods are stunted, and many species which did not 
occur in the littoral districts appear, as also many spongy polypifers 
and large Terebratulze. In the localities occupied by the deep seas, 
such as those of the Colombier and the Reculet, fossils are extremely 
rare ; those found are exclusively cephalopods, and hitherto confined 
to two species of Ammonites and one species of Nautilus. 
The upper group of the Jurassic rocks occupies the highest crests 
and summits, and is formed of a great mass of compact limestones, 
without any interstratified marls. Although the mass is not very 
divisible into sub-groups, that considered equivalent to the coral rag 
of England is stated to be distinguishable both from its position 
above the Oxfordian group and from its fossils. The author subse- 
quently enters into a detail of the various dislocations and contor- 
tions which the Jura may have suffered. 
__ M. Scheerer discusses the plutonic nature of granite and of the 
crystalline silicates associated with it, in a communication translated 
by M. Frapolli. In the first part of this memoir the author enters 
upon an investigation of a peculiar kind of isomorphism, an account 
of which it is difficult to present without the formule and detail 
employed. Referring to the composition of dichroite and aspasio- 
g 2 
