M ON THE MINERALOGY OF THE 



In stating the few particulars which I have it in 

 my power to communicate, respecting the minerals 

 of this district, I shall arrange my observations un- 

 der three heads, corresponding to the three kinds 

 of rocks which chiefly prevail, and to which the 

 others may be considered as subordinate. These 

 rocks are grey-wacke-slate, limestone, and clay-slate. 



I. — Grey- WackeSlate. 



The rocks which I here denominate Grey-ucacke- 

 slate, occur principally in the ridge to the north of 

 the city, where, from having been quarried in seve- 

 ral places, the arrangement of the strata is very di- 

 stinctly exhibited. The rock is termed by the in- 

 habitants Brownstone, from the colour which it usu- 

 ally exhibits. 



The stratification of this rock appeared to me to 

 present some peculiarities which deserve to be men- 

 tioned. I have already stated, that the strata are 

 nearly vertical, and the direction of the stretch uni- 

 form ; and the structure and fracture correspond, as 

 usual, with these characters of position. But be- 

 sides this primary direction of the strata, there 

 may frequently be observed another, or secondary 

 direction, at right angles to the former, by which 

 the vertical strata are divided horizontally. The 

 vertical primary strata experience considerable va- 



