108 Beport on tlie Progress of the Magnetic Survey. [No. 2. 



formation of the calcareous and marly deposit at the bottom of 

 the lakes.* 



Another interesting phenomenon connected with the intertrapian 

 formation is the very regular and horizontal outline shown by the 

 thin line of the sedimentary stratum on the exposed sides of the 

 hills ; and the fact, that though no bending or contortion of the 

 stratum is visible, it may be found at a much higher or lower 

 level on one of the next hills. Erom a careful examination of 

 the localities, I think that this fact can only be due to the ex- 

 istence of extensive faults and to phenomena of subsidence and 

 elevation of whole mountains en masse caused by them. Of the 

 existence of such faults, evident proofs can be found in many 

 localities. 



I finally wish to mention, that the intertrapian lacustrine forma- 

 tion is not confined to the borders of the grand trap mass, but 

 that it can be traced, though often altered and scarcely recogniza- 

 ble, to a great distance to the Westward in the interior of the 

 trap mass. 



4. On the road from Madras to Trichinopoly I had an opportu- 

 nity of examining the cretaceous formation, which seems to be en- 

 tirely limited to this part of India. 



The cretaceous strata cover in these districts an extensive sur- 

 face of country, and the fossil remains are found scattered through- 

 out the formation in many localities. Assisted by my draftsman, 

 Eleazar, and some other of my men, who have now been instructed 

 in collecting similar objects, I have been able to obtain a pretty 

 fine and extensive collection of the cretaceous fossils from very 

 various localities. The whole of the strata from the Pondicherry 

 district down to the most South- Western localities in the Trichi- 

 nopoly district (circumference 120 miles) belong to the same form- 

 ation ; the rocks are quite the same and the fossil remains are 

 nearly identical. 



* I mentioned in tlie first Report for the cold season of 1854-55, that the 

 effusion of the trap in the Deccan had taken place under heavy pressure, probably 

 of sea- water. I now beg to say that it is much more probable that the effusion 

 has taken place at the bottom of extensive fresh-water lakes than at the bottom 

 of the ocean. 



