Bigsby— On the Laurentian Formation. 201 
substance and form, until they wholly disappear, so that in the group 
with which we are now concerned (the very earliest we know of ) 
not only has the original substance of the animal and its habitation 
vanished, but, for the most part, the very form also: and we have the 
residuary elements of the organisms—lime, phosphorus, &c., in 
masses sometimes extraordinarily large, corresponding with the ex- 
tent and thickness of this great group, at least 30,000 feet in Canada 
(Logan), and 30,000 feet in Norway (Durocher). 
The principal of these residuary elements, such as lime, silica, 
alumina, carbon, phosphorus, sulphur, fluor, iron, azote, exist in 
many forms and combinations in these rocks—as beds, seams, and 
veins, or minutely diffused in streaks, bars, or clouds, or altogether 
invisible, throughout certain mineral masses. According to Delesse,* 
a chief authority on this subject, all these elements are essentially 
original; although sometimes they may be contemporaneous with, or 
posterior to, the rocks containing them. 
Lime.—The aggregate thickness of the great limestones of the 
Laurentian series of Canada and the northern parts of the adjacent 
State of New York is about 5000 feet, in bands of from 400 to 
2500 feet, coarsely crystalline, rarely saccharoid, and slightly mag- 
~nesian. In Scotland it is in considerable quantities; and in Norway 
and Finland Durochert found it in beds and lenticular masses 
1000 feet thick (often more), and traceable along the strike for 
many miles. This rock occasionally can only be distinguished from 
the newer fossiliferous marble (Silurian or Devonian) by its being 
more largely crystallized. 
On the north side of the Lower Ottawa Valley Sir W. E. Logan 
finds the marble to emit, on being struck, an overpowering smell of 
carburetted hydrogen;—a fact taken to prove the presence of life 
at the time of deposit. { 
Almost all, if not all, the Laurentian beds, granite, gneiss, horn- 
blende, anorthosite, &c., have lime in their composition. Bischoff § 
and Hunt|| agree with Delesse that lime had taken its place in the 
crust of the earth before the creation of animals and vegetables; and 
we infer the same from the observations of Sir C. Lyell (Princip. 
p- 797). So there always has been a rich provision of this element 
for organic purposes. 
Silica and alumina are most abundant in the rocks of all ages. 
The important chemical services which these substances are now 
known to perform in some geological operations are clearly laid down 
by Dr. Percy in the Lectures already referred to. The subject is too 
manifold for present discussion. 
* Annales des Mines, 6 ser. vol. xxi. p. 165. 
f+ Mém. Soe. Géol. France, 2™¢ sér. vol. vi. p. 34-88; and Bullet. Soc. Géol. Fr., 
n.s. vol. ii. p. 619, &e 
+ Dr. Perey, in his ‘Swinian Lectures’ of 1863 (Dec. 19), mentions a similar 
occurrence in the manufacture, by the humid way, of carbonate of magnesia from 
pure dolomite (so determined by chemical analysis)—so strong and unpleasant an 
odour arose in the process that it had to be abandoned, as a commercial failure. 
§ Geological Chemistry, Engl. edit. vol. ii. p. 183. 
|| Observations on some points in American Geology. 1861. 
