BY LEO A. COTTON. 741 



The Silurian Syste m. 



The oldest rocks are undoubtedly the slates and claystones, 

 which are so widely distributed over New England. All 

 attempts to find fossils in the field have proved unsuccessful, and 

 microscopic investigations have failed to reveal any trace of 

 organic remains. 



The slates vary in colour from dark blue to green, and are very 

 fine-grained. A freshly broken piece may very readily be mis- 

 taken for a fine-grained basalt. They occur in masses frequently 

 surrounded by igneous rocks, and exhibit signs of intense 

 metamorphism. 



At Newstead, the contact of the eastern side of the tin-bearing 

 granite with the slate has given rise to a great development of 

 garnet-rock. The slate here is green in colour, with brown 

 streaks and aggregates of fine brown garnet. 



Again, at the contact of granite and slate, at a point about five 

 miles west from Tingha, a mica-schist is developed containing 

 crystals of garnet up to 3mra. in diameter. The intrusive 

 granite in this locality is the Tingha Granite. 



The evidences of the intrusion of the granite into the slate are 

 (1) Contact-metamorphism, (2) Veins and dykes of granite in the 

 slate, (3) Inclusions of slate in the granite. 



The development of garnet-rock above mentioned is evidence of 

 oontact-metamorphism; another evidence is the common develop- 

 ment of quartzite in the slates near the igneous contacts. 



An excellent example of an intrusive dyke of granite into slate 

 is to be seen in the bed of Darby's Branch Creek at the north- 

 west corner of Portion 214, Parish of Cope's Creek. Here, a 

 tongue of the granite, about two feet in width and several yards 

 long, has intruded a typical slate-mass. One specially noticeable 

 feature is the very sharp contact between the granite and slate. 

 There is no trace whatever of any zone of digested rock. This 

 is worthy of note in support of the application of Daly's theory 

 of overhead s toping to this area. The very marked rectilinear 

 contact also favours this explanation. The intrusive granite is 

 here strongly tourmaline-bearing, this being a characteristic of 



