172 HOLLAND: StVAMALAI SERIES. 



as to nature and origin. But in the present instance we have a rock 

 which has never yet been found as a normal member of the 

 crystalline schists. Although foliated forms have often been de- 

 scribed as local structural modifications of the normal rock, all pre- 

 viously described occurrences of elseolite-syenite have invariably 

 been classed with the eruptives. 



In the Sivamalai occurrence additional interest arises from the 



presence of graphite in the elaeolite-syenite as a 

 Presence of graphite. ,..,,• . 



normal and evenly distributed constituent. 



Graphite is a well-known constituent of many members of the crys- 

 talline schists, and has generally been regarded as the metamorphic 

 product of carbon originally derived from organic sources. Indeed, 

 the presence of graphite in the crystalline schists, and its absence 

 from normal igneous rocks, have led to its being adopted by some 

 as part of the criteria for determining the origin of the rocks in 

 which it is found. In 1896 Professor F. D. Adams, 1 in referring to 

 this question in his report on the geology of a portion of the Lauren- 

 tian area lying north of the Island of Montreal, said, (c the presence of 

 carbon in the form of graphite or any graphitic mineral, disseminated 

 through a gneiss or schist, points to a sedimentary origin, as such 

 substances do not occur in igneous rocks/' 



Here then we are met with a new difficulty, namely, the presence 

 in one and the same rock, as primary constituents, of graphite^ 

 which is supposed to indicate a sedimentary origin, and of elaeolite 

 which is known only as a constituent of igneous rocks. It is evident, 

 therefore, that we must now revise our views as to the origin of one 

 or other of these two minerals,, The nature of this change in our 

 views will depend upon our conclusions as to the origin of the 

 elaeolite-syenite itself. 



To commence with, it must be confessed that there is no- 

 direct evidence obtainable at Sivamalai as to the intrusive nature of 



1 Annual Report, Geological Survey of Canada, 1896, Part J., p. 36* 



( 4 ) 



