GEOLOGICAL HISTORY OF SERPENTINES. LAT 
§ 33. The associated shales and limestones of this gypseous division are, however, gen- 
erally, if not always, highly magnesian. Beck found twenty per cent. of magnesia in 
the limestone overlying the lower range of gypsum-beds, and the precisely similar rocks 
associated with the gypsum at the same horizon in Ontario are dolomitic, the porous or 
vesicular beds being nearly pure dolomite, and other specimens of the limestones and 
shales consisting of dolomite with an argillaceous mixture, the latter sometimes predom- 
inating. * 
§ 34. From a study of the facts before us, it is apparent that we have here evidences of 
the formation by aqueous deposition of a bed of concretionary silicate of magnesia, taking 
the form of serpentine, with a little associated bastite or bronzite, and probably some 
other crystalline silicates. The intimate association of silicate of magnesia with carbonate 
lime is significant, when it is considered that the magnesia which abounds in the accom- 
panying strata is in the form of the double carbonate, dolomite, and serves to illustrate the 
views set forth in § 13, as to the relation between the carbonates and silicates of these two 
bases. It seems probable that we have in this deposit the results of some spring bring- 
ing to the surface, in this locality, waters holding solution in calcareous or alkaline sili- 
cates, which have given rise to a silicate of magnesia, in accordance with the reactions 
already explained in. It is to be hoped that further researches at this geological hori- 
zon may disclose other localities of magnesian silicates similar to that of Syracuse. 
§ 35. We may recall in this connection some facts about the occurrence of magnesian 
silicates in other geological periods more recent than that of Syracuse. Deposits of sepio- 
lite, a hydrous silicate approaching to steatite in composition, are well known in the ter- 
tiary strata of the Paris basin, in Spain, and elsewhere along the Mediterranean. I have 
long since described some of these deposits, and have discussed at length their chemical 
and geological relations. | Mention should here be made of the tale found with the anhy- 
drous sulphate of lime, (karstenite) in the schists at the Mont Cenis tunnel, to be mentioned 
farther on (§ 62,) and also to the association of gypsum and serpentine in the crystalline 
schists of Fahlun, in Sweden. t 
Frejesleben, and, after him, Frapolli, has described the occurrence of a magnesian sili- 
cate which occurs frequently in the mesozoic gypsums of Thuringia, in nodular imbedded 
masses resembling flints in their aspect and mode of occurrence, but composed essentially 
of a soft magnesian silicate, near to tale in composition, and coloured brown with bitumi- 
nous matter. § : 
III—SERPENTINES IN EUROPE. 
§ 36. Having thus passed in review some of the principal facts known with regard to 
the occurrence of serpentines in North America, we proceed to the consideration of the 
same rocks in different parts of Europe, where, as shown in the opening sections of this 
essay, they have long been objects of study, and have been alternately regarded as indige- 
nous and as exotic in character. 

* Géology of Canada, 1863, pp. 347, 625. 
+ Amer. Jour. Sci. [2] xxix., 284, and xxx., 286. 
t See the authors Chem. and Geol. Essays, p. 336. 
% Bull. Soc. Géol. de France, 1847 [2], iv., 837. 
Sec. IV., 1883. 
bo 
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