178 Aiutli/sis of Scientific Books. 



In proportion as the sandstone approaches the trap or whin 

 a marked change is observed in its structure, but not in its 

 composition ; for there is no gradation, no insensible passage 

 of the former into the latter, but the texture of the sandstone 

 becomes more and more compact, with a corresponding in- 

 crease of hardness. Some of the strata, previously straight 

 and regularly parallel, have experienced a very remarkable in- 

 flexion, or dislocation. Thus the tender and friable sand- 

 stone, when it approaches the trap, becomes a mineral like 

 jasper or hornstone. The red and white colours, formerly 

 blended, now separate, and the rock exhibits a ribbony aspect. 

 Higher up the sandstone assumes a more decided quartzose ap- 

 pearance ; with increased density, it becomes more translucid 

 on the edges, its fracture is scaly, and its lustre shining and 

 vitreous. The thickness of its layers also diminishes, as the 

 rock grows more compact; but at the very line of junction, 

 where the quartz see7ns to predominate, we have the same 

 strong effervescence with nitric acid, as in the ordinary sand- 

 stone, which proves the composition to be unaltered, in opposi- 

 tion to those who pretend that the indurated sandstone is a de- 

 posit distinct from the rest of the mountain. 



The disorder and derangement of the sandstone strata near 

 the contact, are no less remarkable ; in fact, these strata, which 

 lower down all preserve the same position and inclination in a 

 regular and uniform manner, appear here contorted and broken 

 in every direction. Sometimes we seebeds, which having retained 

 for some time the common direction, vanish altogether, or in 

 part, to be replaced by masses of trap, in communication 

 with the great incumbent rock ; sometimes these beds, in bend- 

 ing, entirely change their direction, and form with the strata, 

 which have retained their position, a greater or less angle. In 

 other places we perceive large lumps, or even enormous masses 

 of sandstone, or an argillaceous schist, completely enveloped by 

 the whin or diabase, and thus insulated in the middle of this 

 rock. There, however, they still preserve their strata; and these 

 strata have the same thickness, and sometimes the same direc- 

 tion, as those from which they so plainly appear to have been 

 separated, as to leave no doubt of their having once been con- 

 tiguous. 



The trap or whin at the place of junction, exhibits very 

 confused crystallization ; for the crystals of hornblende and 

 feldspar are here so luinute, that they seem to form together a 

 compact homogeneous stone, which might be taken for basalt, 

 if its deep-green colour did not ally its aspect more to that of 

 massive hornblende. This rock effervesces with the acids, 

 owing to the small transparent scales of calcareous spar disse- 

 minated through it. As it recedes from the sandstone, the 

 fock insensibly assumes a mdre brilliant and granular fracture. 



