' MINERALOGY OF ST ANDReWs. 147 



lar, sometimes swell out to a considerable thick- 

 ness, and farther on in their line of bearing, almost 

 disappear. At a place called the Witch-Lake, a 

 bed of sandstone rests upon a horizontal bed of 

 slate-clay. The surface of the bed of sandstone 

 suddenly swells out into a knob, and the slate-clay 

 deposited over this inequality, is seen to rise at a 

 considerable angle on each side in opposite direc- 

 tions, meeting at the top. The inspection of this 

 appearance, will point out the cause of those bend- 

 ings in the strata to the eastward of the city, and 

 convince the observer, that no other circumstance 

 is required to produce those wavings, than an un- 

 even surface of the inferior beds, and that these 

 inequalities of the surface have been produced by 

 the unequal attraction exerted by the beds already 

 formed, to the matter depositing over them. 



I. Sandstone, 



The sandstone occurs in thick beds, which are 

 distinctly stratified. The grains of quartz are 

 sometimes very minute, and the sandstone is fine- 

 grained. In a few instances, the grains of quartz 

 are large, and the sandstone approaches in cha- 

 racters to conglomerate. The cement of all the 

 sandstones in the vicinity of the city, is easily 

 acted upon by the atmosphere, and hence they are 



K 2 



