CHAP. 5.] EOCK FORMATIONS. INFRA-TRAFPEAN GRITS. 57 



The only fossils which the group contains are a few woody frag- 

 ments or indefinite pieces of timber ; and the intimate association 

 of trappean blotches and larger lumps with sub-angular quartz grains 

 in a rubbly calcareous matrix leads to the supposition that the group has 

 au intimate connexion with the earlier volcanic flows, though it cer- 

 tainly differs much from anything that would be called ash. These 

 rocks often weather of a greenish orange, and in some places the 

 color becomes dark and the proportion of igneous materials largely 

 increased. 



Taking it to be partly derived from the waste of the coarse Jurassic 

 sandstone and considering its other characteristics, the group has been 

 looked upon as a local deposit of the lower portion of the stratified trap 

 formation. Its thickness varies up to 1 or 200 feet, being generally 

 less than the latter amount. 



( 57 ) 



