OPHITES AND RELATED ROCKS. 21 



evidence that thermal waters aided the assumed chemical 

 reactions. 



Having now disposed of all the serpentinous structures of 

 " Eozoon Canadense " in strict conformity with the mutations 

 known to characterize the minerals composing them, we shall 

 next offer our explanation of the origin of the calcitic layers 

 which form the " intermediate skeleton " of this reputed fossil. 



With respect to the interchanges between a mineral silicate 

 and a mineral carbonate, often obtaining in ophite, we find that 

 the calcite which frequently holds a place in the layers of chry- 

 sotile is fibrous in certain instances, and retains the original 

 structure of the latter mineral. Generally, however, the charac- 

 teristic rhombohedral cleavage of calcite is developed. This 

 replacement of chrysotile by a mineral carbonate retaining its 

 typical fibrosity, and therefore possessing a fibrous structure 

 similar to that of aragonite, has occurred to us in specimens of 

 ophi-euphotide from the north of Italy, as already noticed in 

 one of our previous memoirs*. 



We have also become acquainted with a similar fact occurring 

 on the shore east of the Lizard, Cornwall, where serpentinyte, 

 undergoing change, contains layers of different colours 

 white and red. Some are coarsely fibrous, others amorphous, a 

 few rudely laminated : often the different kinds may be seen 

 passing into one another. It is only of late that we have 

 observed in the euphotide or " Crouza stone " of the Lizard 

 another modification, consisting of dull white, also blue fibrous 

 layers, with occasionally an imperfect platy structure : in many 

 instances the white layers may be observed assuming a silvery 

 lustre and changing into chrysotile. Moreover, specimens of 

 the latter kind, after having been slightly acted upon by dilute 

 hydrochloric acid, show here and there vacant spaces between 

 the fibres, and other evidences of the removal of a mineral 

 carbonate. 



The mineral silicate, malacolite or white augite, undergoes 

 similar changes. A variety of ophite occurring in Connemara 

 contains layers formed of crystalloids of this mineral. In most 

 instances, besides being widely gashed, and the gashes filled up 

 with calcite, the crystalloids are separated from one another by 

 the same mineral carbonate ; and they exhibit their angles and 

 * Proc. Roy. Irish Acad. vol. xx. pi. xliv. fig, 9. 



