GEOLOGY OF THE GAMPSIE HILLS* 29 



bed contains a much greater proportion of iron 

 than the upper does, and their quantities of horn- 

 blende and felspar also vary. When both of those 

 beds are equally exposed to the external air, the 

 under one is seen to be much more under the in- 

 fluence of decomposition than the upper one. 



This rock is the Floetz^Trap of Werner ; its 

 composition consistsof hornblende, compact felspar, 

 a few scales of mica, some minute portions of 

 iron-pyrites, with an admixture of ferruginous 

 particles, which, in the columnar part of the rock, 

 seem to be but slightly oxidised. 



The sandstone of this district forms a very ge- 

 neral part of its geological composition. The 

 small quantity of cement, which is one of its com- 

 ponent parts, and is the cause of the cohesion 

 among its particles, is a white clay, which entitles 

 it to the denomination of an Argillaceous sandstone. 

 The thickness of the various beds of this rock 

 here, is very unequal, and the layers of its strata 

 are from three to eight feet thick. The upper 

 stratum of this sandstone, upon which the trap 

 rests, is generally of a whitish -grey colour ; but, 

 in passing downwards, it becomes in colour a 

 whitish-yellow, which at last tints down to a yel- 

 lowish-brown, from a slight admixture of iron in 

 its cement. Its granulations of quartz are small, 

 and its texture is rather compact ; but the adhe- 

 sion among its particles, is in general by no means 

 strong. 



