70 Notes, chiefly Geological, of a J ourney thro' the N. Circars. [Jan. 



weight j c the table ; d the two pieces of board, which are made to slide 

 on towards each other. It was found that the superincumbent weight 

 was raised some few inches, and the horizontal pieces of cloth became 

 distorted, like the strata of many rocks. 



We must take into consideration the numerous fissures, through 

 which the immense quantity of trap in India must have been erupted 

 at some remote period, and of which, at present, nothing remains, 

 except the outgoings of these gigantic dykes, on mountains, and in 

 plains, sometimes invisible, because covered with the soil. 



The mass of gneiss, which we have supposed to be enclosed, and 

 compressed between two opposite forces, having been lifted into the 

 atmosphere ; owing to the comparatively speedier decomposition and 

 disintegration of the basalt, which, after a time, falls away, the contort- 

 ed stratified rock is left , either as a solitary block, or as an implanted 

 mass in the detritus of the imbedding rock accumulated round it. 



This must have been the case, with many of the masses of gneiss 

 near Bangalore, Golcondapatnam, &c. ; whose strata, although exceed- 

 ingly disordered, yet have very little trap in their vicinity, which, how- 

 ever, is seen at some distance from them. After what we have stated, 

 we may safely affirm that the frequency of intruding rocks in a forma- 

 tion of stratified ones, produces the contortions in these last; and that 

 when rare, or totally absent, no disturbance in the strata is observed. 



To conclude these cursory notes, we will' give a brief catalogue of 

 the principal rocks, examined during the journey, ranged according to 

 their degree of prevalence. 



1. Gametic gneiss, the felspar sometimes changing into albite or 



2. Porphyry. [adularia. 



3. Hornblende slate and rock. 



4. Sandstone. 



5. Kankar, ancient and modern. 



6. Shell limestone. 



7. Common granite. 



8. Basalt. 



9. Lateritic iron ore. 



10. Sienitic granite. s 



11. Black soil, 



12. Alluvium. 



