626 ON THE RED SANDSTONE OF THE 



The individual strata have sometimes a slaty 

 structure, and this structure is generally parallel 

 with the direction of the stratum, but sometimes 

 it is at right angles to it. It is either straight 

 slaty, or undulating slaty, and the layers are some- 

 times disposed in a concentric manner, and thus 

 the stratum appears composed of a congeries of 

 balls or globular concretions. Some beds of sand- 

 stone have a conglomerated or brecciated aspect, 

 the rock appearing to be composed of blunt and 

 sharp angular fragments set in a basis of sandstone. 

 Eut these are merely apparent fragments, and are 

 to be considered as varieties of structure of the 

 sandstone, probably produced by the process of 

 crystallisation. The careful and connected study 

 of these conglomerated appearances as they occur 

 in sandstone, limestone, quartz, granite, gneiss, 

 clay-slate, and other rocks, leads to very important 

 and interesting conclusions. 



The sandstone contains many different rocks in 

 beds or veins. The most important of these are the 

 following : Conglomerate^ slate-clay, claystone^ 

 clay 'irons tone, trap-tuff, amygdaloid, basalt P 

 clinkstone, felspar, porphyry, greenstone, pitch- 

 stone, limestone and limestone-conglomerate, and 

 coal*. 



■ The occurrence of trap rocks in red sandstone, is stated 

 in the Mineralogy of the Scottish Isles, which I published in 

 1801. 



