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stoue vein is probably only an altered sandstone. The porcellanite 

 alluded to above is a white substance, varying from a dull earthy 

 aspect to that of a white enamel. It occurs of considerable thick- 

 ness along the outer surface of the pitchstone, and is clearly due to 

 a decomposition of this rock. The incipient stages of this decompo- 

 sition show a structure in the rock which otherwise we should not 

 have suspected. The surface is traversed by a series of wavy lines, 

 conforming to one another throughout. This indicates a laminar 

 arrangement within; and it is along these lines that the rock 

 splits completely up in the advanced stages of the decomposition. 



The relations of these various igneous products is further illus- 

 trated by another dike which occurs a little way up this river. A 

 great vein of claystone crossing the bed of the stream shows a 

 distinct passage into jaspery hornstone. The jasper and chert veins 

 in the Tormore pitchstone, with the associated claystones and basalts, 

 place these same relations in a very clear light; and when we view 

 the appearances which they exhibit in connection with those now 

 described, we cannot hesitate to admit that all these products of fire 

 blend into one another; the varying aspects which they assume being 

 due to a slight change in chemical composition, in molecular arrange- 

 ment of parts, or in the rate at which they were consolidated from a 

 state of igneous fusion. 



