30 GEOLOGY OF THE GAMPSIE HILLS. 



Limestone also forms here a very general part of 

 geological composition : it is found in almost every 

 part of this district, and occurs in separate beds, 

 which are, as to depth, considerably removed from 

 each other. In the eastern part of the districtj 

 this limestone is found in two separate beds ; the 

 upper one of which varies in thickness from two 

 to four feet, and is one hundred and seven feet un- 

 der the surface. The second bed has generally a 

 thickness of six feet, and is one hundred and 

 twenty- five feet under the surface. This last bed 

 is in many places extensively wrought by mining ; 

 it produces lime of an excellent quality. The 

 limestones of these two beds, are both of a dark 

 bluish-grey colour ; they are of a glimmering- 

 lustre, and are opake. Their fractures are small 

 splintery, and are somewhat brittle ; they are 

 nearly semihard inclining towards soft. Small 

 portions of iron-pyrites and minute petrifactions 

 of entrochi, are imbedded and thinly scattered in 

 their masses. Both of these beds are much in- 

 tersected by narrow veins of bluish-white cal- 

 careous spar. 



The clays of this district are generally of a 

 dark blue colour, and remarkably tenacious. The 

 shales or slaty-clays are from a dark blue colour 

 to almost that of black \ in some places, this 

 shale admits into its composition a small propor- 

 tion of bitumen and particles of coal-glance. They 

 are of various indurations from very soft to hard. 

 The intervening strata between the two beds of 



