ON THE RED SANDSTONE OF TttH 



and porphyry, associated with masses of granite, 

 containing garnets, syenite, gneiss, mica- slate, clay- 

 slate, hornblende rock, hornblende-slate, amygda- 

 hid, jasper, and red sandstone. Of these sub- 

 stances, the amygdaloid, sandstone, and in gene- 

 ral the porphyries, are of the same species with 

 those which occur in beds and veins in the great 

 red sandstone formation. At the Bridge ofProsen, 

 the conglomerate contains principally masses of 

 porphyry 3,nd amygdaloid, with pieces of quartz. 

 At Blairgowrie, where there are stupenduous 

 rocks of conglomerate, the most frequent im- 

 bedded masses, are porphyry and amygdaloid, 

 with quartz and mica-slate. Near Comrie, they 

 are principally porphyry and amygdaloid. At 

 Callender, the imbedded masses are chiefly por- 

 phyry and amygdaloid J ^nd in A r ran, the con- 

 glomerate contain masses of porphyry and trap. 

 These masses are usually connected together by 

 a basis or ground of smaller fgrains of the same 

 rocks and minerals. Sometimes the imbedded 

 porphyry and amygdaloid is intermixed with the 

 cement at their line of junction, and we observe 

 branches shooting from them into the basis or 

 ground. 



2. Slate-clay. This rock occurs in the sandstone, 

 and also in the conglomerate, in beds that vary 

 in thickness from a few inches to several fathoms. 

 Jts most general colour is reddish-brown, and 



