of the Hyderabad Country. 1 7 



above described will be produced. The same explanation is 

 to be given of the origin of those masses which are found in- 

 sulated in the plains. I imagine that they rest on the summit 

 of what were formerly hills, but which are now completely 

 buried under their own ruins. 



The peculiar arrangement and structure of the quartz and 

 trap in the granite of Hyderabad, afford abundant proofs of 

 the correctness of Mr. Jameson's views of the formation of 

 veins, viz. that they are of simultaneous formation with the rock 

 which they traverse. In the Hyderabad country, we find 

 quartz and trap under the forms of veins, nodules, and moun- 

 tain masses, sometimes perfectly distinct from the surrounding 

 granite, in other instances intermingling with it, and gradually 

 passing into it. With these facts before us, can we doubt that 

 these rocks are of cotemporaneous origin ? 



I have often been surprised that theorists, in their attempts 

 to explain the various phsenomena presented by the crust of our 

 globe, have never employed causes of whose existence we have 

 certain proof, and with whose effects we are well acquainted ; 

 but on the other hand have assumed the existence of causes of 

 which we never had experience, and whose effects we never 

 witnessed. Huttonians assume the existence of a central fire*, 

 which they contend to be the cause of the consolidation of the 

 debris of former hills, and consequently of its conversion into 

 new rocks. But that such a supposition is by no means ne- 

 cessary, is evident from the circumstance, that this consolida- 

 tion often takes place without the assistance of heat. I have 

 already mentioned that the debris of the Hyderabad granite 

 becomes gradually consolidated, merely by pressure; and that 



• The heat of the Huttonians must be an extremely convenient as well 

 as powerful agent, for it can both liquefy and consolidate bodies. At one 

 time it can inject a flood of melted basalt into the superincumbent rocks ; 

 at another time it can consolidate sandstone, and other secondary rocks, at 

 the bottom of the ocean. There are two facts which are very hostile to 

 this theory ;— first, the greater the pressure, the greater is the obstacle to 

 the fusion of a body ; second, the greater the heat, the greater is the op- 

 position to the consolidation of a body. Now, the Huttonian theory requires 

 that the two great agents which it employs, viz. heat and pressure, should 

 act in concert ; the heat to liquefy, or (as occasion may require) to consoli- 

 date bodies ; the pressure to prevent the escape of volatile substances, 

 which might be otherwise dissipated. These two forces, however, must op- 

 pose each other ; for heat is one of the most powerful agents with which 

 we are acquainted in separating the particles of bodies, while pressure 

 brings them closer to each other. The pressure of the ocean, therefore, 

 although in all probability equal in itself to consolidate the debris of former 

 hills into new rocks, may not be sufficient for that purpose, if opposed by 

 a heat sufficiently powerful to liquefy granite and trap ; and a heat that 

 would be equal to the melting of trap at the earth's surface, would be by 

 no means adequate to do so under the pressure of mountains. 



New Series. Vol. 4. No. 1 9. July 1 828. D the 



