148 Boulders of Trap Rocks, fyc, 



seen cutting through stratified rocks, near the Blair of AthoL 

 Another specimen of porphyry, from the Pass of Killie- 

 krankie ; and one from Ben Awe, near Inverary ; and one 

 from near Inverness. There was almost a uniform appearance 

 in all these porphyries while under the heat of the blow-pipe. 

 The same was observed in the porphyries from the gravel. 

 The specimens from the Calton Hill fused with difficulty, and 

 effervescence. The porphyry from the dykes near Blair 

 is of a red colour : it fused under the blow-pipe to a snowy- 

 white enamel, with effervescence. The porphyry* from near 

 Inverary is as red as that from the Blair of Athol ; but it 

 fused into a black glass. 



The porphyry of the Wrekin Hill, near Colebrook Dale, 

 in Shropshire, showed the same reluctance to complete fusion 

 as those from the gravel, and those from Scotland. 



The porphyry of the Wrekin appears to be composed of 

 portions of clinkstone of various sizes, united in a paste, which 

 may be termed a felspathic breccia. It is a hard and beauti- 

 ful rock, of a dark colour : in some places, it approaches to a 

 reddish hue ; it ultimately was fused into an irregular mass, 

 with effervescence. 



Some compact felspars, with small portions of crystalline 

 quartz, from Charnwood Forest, fused with great diffi- 

 culty. These rocks have no crystals of felspar, like many of 

 the porphyries, but are of a dull uniform texture and colour, 

 with scarcely any mineral embedded in them to relieve the 

 sameness, but the few portions of quartz. 



Several varieties of porphyry, of compact felspar with irre- 

 gularly formed crystals of that mineral, fused slowly by direct- 

 ing the whole of the heat, for some considerable time, upon 

 the fragment. These were taken from a different part of the 

 forest whence the former specimens were obtained. 



The greenstone, or sienite of some authors, from Markfield 

 Knoll, fused quickly, with brisk effervescence, into a perfect 

 globule of a glassy black colour. This stone has a large por- 

 tion of hornblende in its mass, probably the cause of its easy 

 fusion. 



The sienite of Mount Sorrel fused very slowly into an 

 irregular shapeless mass. In this the felspar fused into a 

 perfect white enamel, as in the instance above-noticed in the 

 porphyry of Scotland, 



A specimen of compact felspar from Mount Sorrel fused 

 instantly into a black glass globule ; while a fragment from a 

 vein of felspar in the neighbouring sienite could only be 

 superficially vitrified, without altering its angular form. 



A small portion of crystalline felspar, from the great mass 



