Ixii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



are of unusually low specific gravity, and appear to contain no ores 

 of nickel or chromium ; whilst those which belong to the altered Silu- 

 rian rocks yield almost always a small percentage of nickel (rarely 

 more than two or three thousandths of the mineral), and present in 

 many instances deposits of chromic iron sufficiently extensive to be 

 workable. The density of various examples of these latter serpen- 

 tines is given at from 2-546 to 2-607. 



Without impugning the correctness of the conclusions thus drawn 

 for Canada, and whilst admitting that in Europe we may have 

 interstratified masses of a very similar character, as in North An- 

 glesey, and Glen Lochy in Perthshire, one must in passing enter a 

 caution against adopting similar views too generally. 



Yarious, indeed, as the colours presented to the eye by this rock 

 (serpentine) are the opinions oifered to us by geologists and chemists 

 upon its origin and history. Downright uncompromising igneous 

 fusion has been the explanation most readily suggested to observers 

 who, like the Italian and many of the Erench writers, are familiar 

 with the intrusive and fragmentary appearance exhibited by this 

 substance in Italy and the Levant*. The distortion and alteration 

 of the Tertiary strata when in contact with it appear to favour their 

 views ; and some of the Italian geologists, in describing the struc- 

 ture of Tuscany, even recognize several distinct epochs of serpen- 

 tinous intrusion, all of them posterior to the Lower Eocene. 



The idea suggested many years ago by Ereithaupt, that, in analogy 

 with a pseudomorphous mineral which he had determined, it was 

 probable that large masses of hornblende rock had been changed to 

 serpentine, has borne fruit in an abundant crop of speculations. 

 Thus H. Miiller, G. Rose, Bischof, and others derive many of the 

 serpentines of Saxony and Southern Germany from the metamor- 

 phism of eklogite, of granuKte, and of gabbro or euphotide. 

 Tschermak looks upon that of Giimbelberg in Moravia f as pro- 

 duced by the decomposition of a rock of anorthite and augite ; and 

 Bischof suggests that the celebrated serpentine mass of Snarum, in 

 Norway, is the result of a transformation of a mass of olivine. In 

 fact the chemical probability of hydrated silicate of magnesia being 

 produced by various decompositions, and the tendency of these ophi- 

 olitic rocks to appear geographically associated with diorite, gra- 

 nulite, gabbro, chlorite-schists, and eklogite, seem to offer a premium 

 to the ingenious for inventing an almost infinite series of possible 

 combinations and permutations. In the curiously patterned stripes 

 and anastomosing veins which so many varieties of serpentine pre- 

 sent, and in the numerous minute crystallized minerals (garnet, mag- 

 netite, chromic iron, &c.) which are disseminated in them, there 

 appear to lie the materials for a history ; and yet we may venture 

 to express a doubt whether, when we see a mountain mass consist- 

 ing at one end of serpentine and at the other of diorite, with a 

 gradual passage in the intermediate part, we are obliged to con- 

 clude that there has been historically an actual transition from the 



* Vide also Fiedler, ' Eeise in Grriechenland,' Leipzig, 1840, p. 432. 

 t Sitzsungsber. d. Wien. Akad. 1860, p. 132. 



