GEOLOGICAL RELATIONS AND ORIGIN. «73 



elaeolite-syenite. The rock is foliated parallel to the direction of th ! 



surrounding crystalline schists, and, so far as 

 Evidence of igneous b de out j fc occurs merely as lenticular 



OTigm by analogy ot *•■*" ** » J 



structure and cornposi- masses But on the other hand, examination of 



tion. 



the rocks in the field reveals many points 

 which are characteristic of igneous ^ and especially of eruptive, masses 

 of elaeolite-syenite. For instance, the ordinary foliated, fine-grained 

 rock is traversed by very, coarse-grained veins composed largely of 

 elaeolite and felspar, and with only small quantities of the ferromag- 

 nesian silicates, graphite and iron-ores. At their edges these coarse 

 veins pass gradually into the fine-grained rock and frequently include 

 u horses" of the latter; in fact they are strictly comparable to the 

 so-called contemporaneous veins so commonly found in plutonic rocks. 

 Again, we frequently meet with basic fine-grained autoliths in 

 which the ferromagnesian constituents are concentrated— pheno- 

 mena also common to igneous masses. Chemical analysis shows the 

 Sivamalai rock to resemble the ordinary elaeolite-syenites in com- 

 position, and but for the graphite it would agree also in mineral com- 

 position, with many previously described eruptive forms ; even in the 

 characters of the felspars and ferromagnesian silicates the Sivamalai 

 mass shows the peculiarities which serve to distinguish the remark- 

 able family of elaeolite-syenites from the commoner plutonic rocks. 

 Calcite occurs well distributed through the rock, apparently as a pri- 

 mary constituent similar to that in the elaeolite-syenite of Alno, 

 Sweden, and of Hastings county, Ontario. Finally, the Sivamalai 

 rock, like most elaeolite-syenites, is associated with an augite-syenite, 

 which resembles Brogger's laurvikite in containing olivine and 

 zircon, as in the well-known occurrences of South Norway. 



Against the presence of graphite we have, therefore, a large 

 number of points of agreement between the 



Significance of foliation. 



Sivamalai mass and the usual type of eruptive. 



elaeolite-syenite, and as for the gneissose structure, if not a distinctly 



secondary character, it is at most the result of an accident attending 



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