256 



THE CANADIAN NATURALIST. 



[Vol. ix. 



crystals and grains of olivine, augite (mostly in crystals) and a 

 small proportion of plagioclase feldspar and magnetite. But 

 while the augite mostly remains fresh, a large part of the olivine, 

 which appears to be the most abundant constituent of the rock, 

 has been altered to serpentine. Most of the olivine crystals and 

 irrains retain a nucleus of the unaltered mineral, showino- the 

 characteristic rifts, and the outlines of many crystals which are 

 partly or entirely converted into serpentine are still perfectly 

 sharp. In the accompanying figure (Fig. 2) a represents a group 

 of crystals which are mainly composed of serpentine, but show 

 nuclei of olivine and a few opaque grains probabl}^ of magnetite ; 

 h is an irregular mass also partly changed to serpentine ; c repre- 

 sents a crystal which has been entirely converted into serpentine ; 

 while d is an almost perfectly fresh crystal of olivine. 



Fio. 2. 



On further alteration such a rock might be almost entirely 

 converted into serpentine. Such a change has been observed 

 elsewhere, as, for example, in the case of many of the Wurtem- 

 berg basalts, which are said to be " little more than serpentine 

 rocks containing some magnetite, since the olivine and augite 

 which composed the basalt are changed into serpentine." 



In this country we have other examples than those already 

 given of the production of serpentines by the alteration of other 

 rocks. That such is the origin of many of the serpentin'es of the 

 Eastern Townships there can be little doubt. Tiie fact of their 

 being commonly chromife;ous suggests that at least they may 

 have been derived from such peridotic rocks as Iherzolite, dunite, 

 olivine-aabbro, &c. 



Published 29th December, 1879. 



