UPPER SECONDARY ROCKS. 



97 



the tertiary group, or those lying above them, not 

 Only by their chemical character, being chiefly creta- 

 ceous (carbonate of lime), but by their greater com- 

 pactness ; a want of conformity in their strata (the 

 secondary being rarely parallel to those of the su- 

 perior order), and also, as has been already stated, 

 by a great difference in their organic remains. The 

 formations which fall under this group may then 

 briefly be described in the following order in the as- 

 cending series : 



1. New Red Sandstone. I 2. Oolitic. 



3. Green Sand. | 4. Cretaceous or Chalk. 



The new red sandstone is so called to distinguish 

 it from that found among mountain rocks, called 

 old. Its prevailing character is silicious, but it of- 

 ten comprises calcareous beds of considerable ex- 

 tent. Bakewell divides this rock into three series, 

 viz., the upper, the middle, and the lower beds. These 

 divisions are often well marked by intervening beds 

 of limestone ; where such do not occur, they are so 

 blended as to be undistinguishable. It is the general 

 opinion of geologists, that this rock, together with 

 the conglomerate beds found in it, was formed by 

 the violent disintegration of the older rocks, and par- 

 ticularly of trap rocks, that were protruded at the 

 era of some great convulsion, which broke down a 

 large portion of the ancient crust of the globe, and 

 spread the debris far and wide over the bed of the 

 existing ocean. This appears from the fact that 

 fragments of the older rocks occur in the different 

 beds of this sandstone, and that some of the beds 

 are almost entirely formed of such fragments. This 

 mode of formation is supposed to account for the 

 great diversity both in the nature and thickness of 

 the beds in different districts. Some geologists 

 maintain that the disintegrating causes which broke 

 down part of the ancient rocks, and thus spread 

 abroad their ruins, acted at successive periods of 



