MIDDLE DISTRICT OF SCOTLAND. 62S 



the whole mass of strata is in its original posi- 

 tion, and composed of a series of distinct con- 

 cretions, in each of which, the layers or ap- 

 parent strata vary more or less in position, in 

 these respects resembling what we observe in 

 greenstone, porphyry, and other similar rocks. 



Enormously thick but short beds of sandstone, 

 are sometimes surrounded with thin strata of 

 sandstone, slate-clay, and other rocks. It occasion- 

 ally happens, that in a ravine or valley, the one 

 side will present a vertical face of red sandstone, 

 without any marks of stratification, thus intimat- 

 ing the presence of a thick massive bed, while 

 the opposite side will exhibit numerous thin beds 

 of sandstone and slate-clay, dipping towards the 

 mural precipice. Here all the rocks are in their 

 original position ; there has been no sinking of 

 strata on the side with the mural precipice ; 

 for, the thin strata, if continued to the pre- 

 cipice, would either rise toward it, or termi- 

 nate suddenly upon it without any change in 

 their direction, just [as we observe to be the case 

 with the thin sandstone strata, where they come 

 in contact with thick beds of the same rock. 

 Many of the pretended sinkings and shifts enu- 

 merated and described by geologists, are of this 

 description. Indeed it would appear, that these 

 mechanical actions are much less frequent than 

 has been generally imagined, and that the crust 



