ON STRATIFICATION. 



225 



5. Certain appearances in trap rocks are illus- 

 trative of the simultaneous formation of strata. 

 In these rocks, we sometimes observe small im- 

 bedded portions of limestone and slate^clay, so in- 

 termixed with trap, as to prove their cotempo- 

 raneous origin with it : in other instances, the 

 limestone and slate-clay appear in the form of 

 small layers, alternating with each other, and fair- 

 ly included in the trap : and I have observed 

 in some districts, beds of limestone, slate -clay, 

 and clay-ironstone, alternating with each other, 

 and of considerable extent ; and all of them 

 fairly included in an immense bed of trap. The 

 quartzy sandstone which so often accompanies 

 trap rocks, presents similar appearances with the 

 limestone, &c. just mentioned. Other formations, 

 as I shall particularly explain in a future commu- 

 nication to the Society, present the same remark- 

 able appearance of series of strata being contain- 

 ed in one great stratum or bed, or in a series of 

 strata of one species of rock. la the cases just 

 stated, trap, limestone, slate- clay, and clay -iron- 

 stone strata, have been formed at the same time ; 

 but the limestone, slate- clay, and clay-ironstone, 

 being included in the trap, bear the same relation 

 to it, that crystals of quartz do to the basis in 

 which they are imbedded, or cotemporaneous por- 

 tions of gneiss to the granite in which they are 

 contained. 



VOL. II. P 



