and their Contact Zones. 



61 



as I know, contain no dykes. These dioritic and 

 granitic rocks form a whole, as regards the sediments 

 into which they have intruded, but in respect to each 

 other, they are all also intrusive, and, I may say with 

 some confidence, that the more hornblendic varieties 

 are the latest in occurrence ; so that we have the mental 

 conception of a first invasion by quartz diorites and granites, 

 followed by quartzless diorites, and these again by 

 amphibolites, and bordered, except in the south, by a margin 

 of quartzose plagioclase or orthoclase rocks whose gneissic 

 structure is probably one of the phenomena due to contact 

 with the sediments. Finally, we must also perceive that the 

 metamorphism produced has been the result of all these 

 intrusions, and, therefore, an intermittent process. 



The Metamorphic Contact Rocks. 



In describing the intrusive granites and diorites I passed 

 from their contact with the sediments to them. I now 

 reverse the process, and having briefly described the inter- 

 relations of the intrusive masses, proceed to describe these 

 altered sediments and their mutual relations, into which the 

 former have intruded. 



If we commence at the termination of the gneissic or 

 granitic rocks into which the true quartz diorites appear to 

 graduate near the contact, we shall find that the sedimentary 

 rocks present to us certain appearances of alteration, which, 

 broadly speaking, are applicable to the whole of the contacts 

 surrounding the igneous masses. I may take an example 

 from the lower part of Riley's Creek. 



tp h o d 6 f% ~k\\ I nru 



frw 



Diagram No. 1. — Section across Contact at Lower Riley's Creek. 



Scale, about 40 chains to one inch. 



