2o6 The Ottawa Naturalist. [February 



offered to the Logan Club for the consideration and discussion of 

 its members. 



As stated by Dr. Adams and the writer in a previous paper, 

 read before the Geological Society of America at the winter 

 meeting of 1896, the rocks exposed within the area under 

 examination belong to several sub-divisions of the Arch?ean. 



I. Laurentian ; 2nd, Grenville Series ; 3rd Hastings Series. 



The Laurentian covers by far the greater part of the area 

 in question. Briefly stated it is now believed to consist of an 

 extremely complicated series of intrusions, very approximately 

 synchronous, representing plutonics of relatively greater or less 

 basicity. These gave rise to a complex of irruptive rocks, which 

 differ in no essential respect save that of a somewhat per- 

 sistent foliation from the normal or massive types of the granite, 

 diorite and gabbro families. The Grenville Series, on the other 

 hand, comprises a great development of crystalline limestones, 

 associated with certain fine-grained gneissic rocks whose general 

 appearance and microscopic structure mark them as highly 

 altered sedimentaries. In regions further to the east, where pre- 

 cisely similar rocks have been examined in detail by Dr. Adams, 

 it has been shown that they likewise possess a chemical com- 

 position closely analogous to that of clay-slate. 



The relations of these two members of the Archaean in 

 Central Ontario, suggests in the strongest manner that 

 in the Grenville Series we have a truly clastic group of 

 strata which has slowly sunk down into and been invaded by 

 much greater volumes of the granites and gneisses of the 

 Laurentian when these latter were in a plastic condition. The 

 limestones are very highly metamorphosed, having in most cases 

 become thoroughly recrystallized, and now present the characters 

 of coarse, although often more or less impure marbles. The con- 

 tact between the gneisses and granites of the Laurentian on the 

 one hand and the limestones and associated rocks of the Gren- 

 ville Series on the other, is, wherever examined, one of intrusion. 



Towards the south and south-east, the region is uuderlaid 

 by rocks of the so-called Hastings Series, consisting principally 



