350 



Geology of the Deccan. 



[Oct. 



from the amygdaloids above ; but its great thickness usually preserves 

 it from obliteration, and it rises from the wood below with majestic 

 effect, its black front being finely contrasted with the rich and lively 

 green of its sylvan associate. It is these strata, arranged in slopes and 

 scarps repeated three or four times, and so commonly met with in in- 

 sulated and other mountains in Dukhun, that constitute the amazing 

 strength of the hill forts of the country, leaving a succession of natural 

 walls encircling a mountain. This feature did not escape the observa- 

 tion of Captain Dangerfield in Malwa, who says, " From the great dif- 

 11 ference in the resistance made to decomposition by these trap and 

 " amygdaloid beds, their exposed ends acquire a very distinct degree 

 " of inclination and character ; the amygdaloid forming a great slope, 

 " and affording a loose mould covered with vegetation, the trap retain- 

 " ingits original perpendicularity and dark bareness."* 



In the alternation of the strata there does not appear to be any unifor- 

 mity ; but the general level, thickness, and extent of a stratum are 

 preserved, as in sedimentary rocks, on both sides of a valley ; the 

 basalt and hardest amygdaloids being traceable for miles in the paral- 

 lel spurs or ranges ; but the imbedded minerals, and even the texture, 

 vary in very short distances. 



Columnar Basalt. — A great geological feature of Dukhun is 

 the occurrence of columnar basalt. The basalts and hardest 

 amygdaloids run so much into each other that the line of 

 separation is not always readily distinguishable, excepting of 

 course the lines of horizontal stratification. I obs'erved the pris- 

 matic disposition more marked and perfect in the basalt strata 

 than in the amygdaloids, and the more or less perfect development of 

 determinate forms was dependent on the compactness and limited 

 constituents of the rocks. Basalts and amygdaloids, however com- 

 pact, with many imbedded matters, rarely formed columns. Perfect 

 columns were generally small, of four, five, or six sides ; but the pris- 

 matic structure sometimes manifested itself in basaltic and amygda- 

 loidal columns many feet in diameter. A bare mention of the places 

 where they occur will testify to their extended localities. 



On the low table-land of Kurdah, near Serroor, between sixty and 

 seventy miles east from the ghats, columnar basalt occupies an area 

 of many square miles. Small columns are seen in most of the slopes 

 of the very narrow sinuous valleys of the flanks of the platform, and 



* Malcolm's Central India, Appendix, p. 322, 



