92 



ON THE MINE11ALOGY OF THE 



The beds of limestone are of considerable ex- 

 tent, appearing on the surface nearly a mile in a 

 direction across the strata. These beds are divided 

 rather indistinctly into strata, and are with difficulty 

 quarried. 



Subordinate to this compact limestone, there oc- 

 curs common compact dolomite, or Magnesian 

 Limestone ; having the colour intermediate between 

 yellowish-white and ash-grey, — the lustre glimmer- 

 ing inclining to glistening, — and the fracture fine 

 granularly foliated, — it is harder than the compact 

 limestone. 



In some cases, the dolomite appears in the com- 

 mon limestone in the form of a thick bed, sel- 

 dom continuing to any great extent. In other pla- 

 ces it appears as large irregular-shaped contempo- 

 raneous masses. 



It is frequently full of drusy cavities, the sides 

 of which are covered with different kinds of crys- 

 tals. In this state it is usually darker coloured and 

 more brittle. 



The most common sort of crystals found here are 

 of brown-spar, or pearl-spar, of the same colour as the 

 surrounding rock, sometimes of a brownish orange. 

 Super-imposed upon these may be observed crystals 

 of dolomite-spar, in the form of oblique rhombs. 

 These crystals are middle-sized, — occur from trans- 

 parent to opaque, and in some cases are rough on the 

 surface. 



