io6 



Granite. — The granite, though limited in extent, is 

 important, as it probably indicates conditions that favoured 

 the development of asbestos. It forms hills in the north- 

 eastern part of Coleraine, dykes in most of the mines, and, 

 in places, isolated masses grading into the enclosing diabase 

 or porphyrite. These isolated masses are, probably, 

 primary segregations. 



Structural Relations. — The rocks of the Thetford 

 series are obviously intrusive in their relations to the 

 enclosing sediments. Evidences of this are: alteration of 

 the sediments in the outer contact zone; deflection of 

 their dip and strike; and development of contact breccias. 



The alteration of the sediments is sometimes shown 

 by a hardening of a band near the contact, producing a 

 hornstone rim. The grey slates are often given a rusty, 

 reddish colour, due apparently to the oxidation of sulphides 

 developed near the contact, while the originally red Sillery 

 slates are usually bleached to pale pink. Fragments in 

 the breccia, and larger portions of sediments near the 

 contact, show partial absorption by the igneous magma. 

 Some of these rocks still preserve the lines of foliation of 

 schists on weathered surfaces, but on freshly broken faces 

 they cannot be distinguished from the enclosing, or 

 adjacent, igneous rock. 



Dykes are very rare, and altogether there is a very 

 noticeable absence of evidence of any violent eruption. 

 The intrusion seems to have progressed slowly, and without 

 any marked cataclysmic action. The contact is thus of 

 the batholithic order. 



The bodies of igneous rock appear to take two prin- 

 cipal forms. From Broughton mountain to Little Nicolet 

 lake, where the igneous belt crosses the stratification 

 somewhat obliquely, the intrusions occupy elliptical or 

 rounded areas, bordered by breccia, and giving evidence 

 of downward enlargement. With the exception of one 

 district, and two doubtful intervals, they form a continu- 

 ous mass, and so are interpreted as being a batholith, or 

 very thick laccolith. 



In other parts of the district, the boundaries of the 

 intrusions conform more closely to the stratification, are 

 generally brecciated on one side only, and occupy long 

 narrow areas. In cross section they can sometimes be 



