372 PRIMARY LIMESTONE. 



most conspicuous and common. For the con- 

 venience of the student, they are all noticed again 

 under the head of Conglomerate Rocks; 



The colours in these varieties are infinite, 

 and the peculiar disposition of the parts gives 

 rise to many well-known ornamental marbles. 



Independently of the general colours before 

 alluded to, and those derived from the intermix- 

 ture of the minerals just enumerated, the primary 

 limestones present a great diversity of aspect from 

 the passage of veins, as they are frequently 

 fissured in intricate directions, and the fissures 

 are generally filled with a pure white carbonat. 

 In these cases they also occasionally become con- 

 glomerates. Further, it may be added that the 

 various shades of grey are among the prevailing 

 colours. 



Besides the minerals which are enumerated 

 in the second division, because they sometimes 

 abound so as essentially to modify the character 

 of the rock, others occur imbedded in limestone 

 as their occasional repository. The following 

 catalogue contains those most usual, including 

 the substances which occasionally enter in larger 

 proportion. 



