May 1861.] 



Altered Rocks. 



53 



operations, the fluid Trap while cooling having taken up small 

 fragments of Felspar, &c, from the sides of the chasm it invades. 



On putting forth this paper I anticipate being met with an 

 objection from Mr. Dela Beche who states " the term 4 altered 

 rocks' is at present exclusively applied by Geologists to that modi- 

 fication of mineral structure which has taken place in rocks since 

 their production through the agency of heat ; it being understood 

 that the heat has never been sufficiently intense to produce 

 fusion." In my own defence, if it be necessary to enter into a 

 defence after the foregoing account of what I have actually seen, I 

 beg to remind Geological readers of the following facts. 



1st. The Oolitic rocks and chalk in junction with Trap, have 

 been found fused and converted into crystalline marbles. 



2nd. Coal has been converted into coke through the agency of 

 the enormous heat of the Trap. 



3rd. Sulphur has been sublimed. 



Dr. Buckland and Mr. Conybeare witnessed instances of the 

 conversion of chalk into crystalline limestone by basalt in the 

 country of Antrim. If I have made correct inductions from what 

 I have witnessed in the altered rocks, a strong temptation is held 

 out to ascribe the formation of Gneiss and Hornblende Schist 

 which passes by imperceptible degrees into Granite and Syenite, 

 to the agency of incandescent Trap matter moving with enormous 

 velocity across the Granite and Syenite. 



To me it seems more philosophical to conceive that such an 

 operation as I have described, changed the crystalline rocks into 

 Gneiss and Hornblende Schist, than to employ a combined theory 

 of aqueous deposition and subsequent Plutonic action, as some 

 Geologists have done. 



