BY W. N. BENSON. 583 



enstatite formed large plates several inches long, with poikilitieally 

 included olivine. 



Associated with these peridotites, was a small amount of gabbro, 

 which occurs chiefly on the top, and on the southern slope of 

 Chrome Hill, on the western side of the peridotite. On the hilltop, 

 it is very coarsely pegmatitic with large, grey-brown diallage, 

 "saussuritised" felspar, and sometimes a little chromite. Large 

 masses of chromite occur here with pseudophite, and coarse-grained 

 rocks composed of chromite and smaragdite also occur, as well as 

 rocks composed entirely of coarse bastite-crystals. The last two 

 are rare. Down the slope, the rock is sometimes almost undecom- 

 posed, and the great basicity of the original felspar can be deter- 

 mined. A few instances of the prehnitic alteration of the felspars 

 are also to be found. 



One of the very few instances of serpentine occurring west of 

 the great serpentine-line, is found on the Peel River, near Warden's 

 homestead (Portion 9, Parish Dungowan). Only a few square 

 yards are exposed in the river-bank, and alluvium covers the 

 remainder, so that its relations are unknown. Probably it occupies 

 a fault-plane, but, so far, the fault has not been sought on the hill 

 across the river to the south, where it should occur if present. 



The original peridotite has now been more or less completely 

 altered, and it is the variety and sequence of these changes that 

 gives this locality its unique interest. The subject will be fully dis- 

 cussed from a petrographical standpoint later; at present, merely 

 the field-facts will be stated. 



(a) Mechanical Alteration. — This consists in converting the 

 rock into the well-known schistose material. It may be either com- 

 plete or partial, in which case large or small nodules of massive 

 serpentine remain imbedded in the sheared mass. This process has 

 naturally taken place, to the greatest extent, on either side of the 

 intrusion, but particularly on the eastern. Thick schistose bands 

 have a massive central core. 



(b) Chemical Alteration. — This may be considered as: (^hydra- 

 tion (serpentinisation) ; (2) carbonation; (3) silicification ; (4) 

 leaching. The last three are more or less related together. 



