234 Geology of the Neilg /terries* [No. 12, new series. 



fawn color, with white, black, and dark brown spots and streaks. 

 Phillips calls this mineral Porcellanite, and does not consider it a 

 true jasper. It has the appearance of baked clay. 



(h.) The crystals of Sahlite (a variety of Augite) being partial- 

 ly decomposed, have lost much of their original character, the 

 primary form of crystallization and the green colour however still 

 remain The longer axes of all the crystals maintain the same 

 direction in the gangue. 



A particular notice of the Traps is deferred to a succeeding 

 paper. 



Having thus described the materials composing and combined 

 with the vein of Siliceous Schist, I will endeavour to account for 

 its origin and singular conditions. 



It is easy to conceive, at some remote period in the Geological 

 era, that the primary rocks by some internal convulsion were rent 

 into fissures and chasms, subsequently filled, as in the present in- 

 stance, by Trap, and Siliceous Schist, &cc. ; but it is more difficult 

 at once to determine whether the Trap in its passage through the 

 chasm converted the sides of it (under present circumstances con- 

 sisting of Syenite) into the Schist, or to pronounce whether the 

 Siliceous Schist was in the first instance injected from below in a 

 mass of soft matter, subsequently partially indurated by time and 

 altered by Trap afterwards. 



In other words to decide whether the Trap is of contemporane- 

 ous origin with the Schist, or the Schist older than the Trap. 



In favor of the first hypothesis is the important fact that the 

 sides of the chasm in the Syenite (exposed in a mass of rock crop- 

 ping out from the side of the Hill) affect the Sehistose structure : 

 while on the other hand is the following evidence in support of the 

 theory, that the Trap must be of more recent origin than the 

 Schist, viz, its passage through that rock and the alteration it has 

 produced in converting it into jaspers. 



These two views are so equally balanced that it is impossible to 

 decide in favor of either of them, to the utter exclusion of the 

 other. I therefore come to the conclusion that the chasm was first 

 filled with Siliceous Schist, and the Trap afterwards obtruded 



