4 Canadian Record of Science. 



limestones had been invaded by it or had sunken down 

 into it while in this plastic condition. Which one of 

 these suppositions represents what has actually taken 

 place is a difficult matter to determine. It might be that 

 both are true in degree. Be that as it may, the action 

 on the limestones would be practically the same, and 

 certain it is that the great part of the intrusion is 

 identical in character with truly intrusive igneous rock. 

 There is still another possible explanation of the cause of 

 these phenomena but it can only be referred to farther on. 



Two specific problems now present themselves : the 

 origin of the basic contact rocks, and the true character 

 of the seeming inclusions. Specimens of the various 

 rocks were collected by Dr. Adams, and some of them 

 have been handed to the writer for investigation, in order 

 that their mineralogical composition and character might 

 be determined, and a comparison instituted between the 

 several basic varieties themselves, and the limestones of 

 which they are apparently the altered representatives. 



Although the problems are distinct, several facts are 

 encountered which render their exact and definite solution 

 difficult. The rocks are not infrequently concealed by a 

 mantle of drift, which is often thick ; the contact itself 

 is by no means sharp, but is instead, a brecciated zone of 

 granite and of the invaded rocks in varying stages of 

 alteration, and its demarcation and study would be a 

 serious matter even if it were everywhere exposed ; and 

 fully as important as the two preceding facts, is the one 

 that, due to the frequent similarity in appearance of rocks 

 quite different in composition, and to the complexity of 

 the relations generally, it is often almost impossible to 

 realize fully, while in the field, the importance and 

 significance of such facts as are observed — this can only 

 be done later, when thin sections of the specimens can be 

 examined. 



The limestones are the same white or pinkish crystal- 



