SERPENTINES AND DIABASES 513 



The igneous origin of the serpentine was also first pointed out by 

 Doctor Adams in the same publication. In a specimen from Melbourne 

 the rock was found to be wholly reduced to serpentine, with the exception 

 of a few grains of bastite orother mineral derived from rhombic pyroxene. 

 In specimens from townships of Ham remnants of the primary olivine 

 were also found. 



The following analysis of serpentine of the Eastern townships are taken 

 from the Geology of Canada, 1863 : 



Orford. Ham. Bolton 



Silica 40.30 43.40 43.70 



Magnesia 39.07 40.00 ' 40.68 



Nickel oxide 20 



Ferrous iron 7.02 3.60 3.51 



Water 13.14 13.00 12.45 



100.00 100.00 100.34 



Hornblende granite also occurs within this belt and is commonly in- 

 trusive through the serpentine. In other parts it seems to form an acid 

 portion rather sharply differentiated from the magma of the parent rock 

 of the serpentine. It has been described by Doctor Adams* as composed 

 esentially of quartz, orthoelase, plagioclase, and hornblende, with a little 

 titanic ore. It is also noted as showing a peculiar alteration of the horn- 

 blende. Where this mineral comes in contact with the quartz it displays 

 a development of fibrous forms terminating in tufts of fine needles run- 

 ning into the quartz; opposed to this marginal facies when in contact 

 with quartz, hornblende displays an ordinary even edge when in contact 

 with the fieldspar. 



Dikes of this rock in cutting the serpentine are considered by miners 

 to be indicative of the occurrence of the good asbestos. Whether the 

 fracturing of the serpentine accompanying the intrusion of the granite 

 has in any way furnished lines of weakness for the formation of asbestos 

 veins has not yet been established. 



Serpentine apparently quite different in origin occurs at several places 

 within the porphyry-andesite belt already described. Here within a dis- 

 tance of 10 to 20 feet well exposed. rock may be traced from a quartz 

 porphyrite to serpentine carrying narrow veins of asbestos. Such occur- 

 rences are found in the townships of Ham, Leeds, and several other places 

 within the volcanic belt. So far as yet known, none of these are of large 

 extent. That in Leeds is probably half a mile in length. The importance 

 lies, however, in showing the range of magmatic differentiation, and con- 



* Op. cit. 



XLVI — Bull. Geol. Soc. Am., Vol. 17, 1905 



