94 



ON THE MINERALOGY OF THE 



sists of a number of smaller ones. The surface of 

 the columns is a little rough, and the angles blunt. 



At the same place, there are numerous crystals 

 of quartz, consisting of six-sided prisms, terminated 

 by six-sided pyramids, imbedded in the limestone. 

 These crystals are nearly opaque, dull, and the angles 

 are blunt, They consist of concentric layers of 

 quartz and limestone. In one of these crystals, 

 not more than -J of an inch in thickness, I have 

 counted nine different layers. It is obvious, that, 

 in this case, the matter of the quartz, though in 

 very small quantity, has been able to act upon the 

 calcareous matter, in such a manner, as to impart 

 its own natural arrangement, instead of the struc- 

 ture peculiar to calcareous minerals.*— This sub- 

 ject will be resumed in a subsequent part of the 

 paper. 



Not far from the city, and to the south of the 

 Lunatic Asylum, there is a bed of Hornstone* It 

 varies in colour ; being light brownish-red, where re- 

 lated to the brownstone *, and bluish-grey, where in- 

 fluenced by the limestone ; the fracture is fine splin- 

 tery, approaching to. conchoidal, and it is translu- 

 cent. 



The bed is only a few feet in thickness, and pre- 

 serves its direction to a considerable distance, and 

 with great regularity. In its immediate neigh- 

 bourhood, the limestone is much mixed with silice- 

 ous matter ; and, in some places, appears in a state 

 of decomposition, the calcareous portion having 



