The Monteregian Hills. 



217 



bowlders are scattered about. These are largely gneisses 

 from the Laurentian highlands, but some of them are 

 plutonic rocks from other hills of the Monteregian group. 

 The plain about Mount Johnson is, however, stated by 

 Ells, who has examined this district, to be underlain 

 " presumably " by rocks of the Utica-Lorraine division of 

 the Lower Silurian. 



On ascending the mountain the first rock which is 

 exposed above the drift mantle is a very fine-grained dark 

 hornstone, uniform in character and lying in undisturbed 

 horizontal beds. It can be seen at intervals all around 



Fig. 3. — Mount Johnson, as seen from the southwest, showing 

 limits of the several rock types composing the mountain. 



the base of the mountain, forming a sort of collar, and is 

 undoubtedly a shale such as that usually constituting the 

 Utica formation, here however altered by its proximity to 

 the intrusion. This shale wherever seen lies flat and 

 abuts against the igneous rock of the intrusion, being cut 

 sharply off by it, but not tilted or upturned. The upper 

 limit of the shale is shown in the accompanying photo- 

 graph of the mountain. 



The mountain above this hornstone collar is made up 



