196 f RETACEOUS ROCKS OF S. IXDIA. [PaRT II. § 2. 



the sea, and regur would only be deposited to the South of the ridge 

 when either continued upheaval had raised another and outer ridge 

 above the sea level, or a sand spit had been formed, converting the 

 lower area in its turn into a lagoon. 



There is, however, one fact which presents itself as a difficulty to the 

 above hypothesis ; viz., that, supposing the country to be covered in 

 the first instance with the sandy soil even on those areas which are 

 subsequently covered with regur, we should expect a priori to find, in 

 most cases at least, a deposit of the former underlying the latter, 

 but this I have only observed in a single case. I can only suggest to 

 account for this that seeing the small average thickness of the red soil, 

 and remembering that there is frequently evidence of the material of 

 underlying rocks when soft being washed up into the lower part of the 

 regur, that the original deposit of sand has been in like manner inter- 

 mixed with the subsequently formed regur, possibly by the movement 

 of the water over the shallow bottom of the lagoon during the ebb and 

 flow of the tides. Regur always contains a large proportion of sand, 

 and the usual characteristic red color of the sandy soil (due to the per- 

 oxidation of the magnetic iron it originally contained) would be obscur- 

 ed by the coloring matter of the rggur, even supposing the peroxidation 

 of the iron had not been checked by the presence of organic matter in 

 the latter soil. The single instance in which I noticed regur resting on 

 the sandy soil was to the South-west of Chellumbrum, where the under- 

 lying rock is in all probability Cuddalore sandstone. I have previously 

 noticed the prevalent greater thickness of sandy soil on this group 

 of sandstones, and I infer therefore that in this case the deposit of the 

 red soil was originally too thick to be washed up into the regur, as 

 occurred in the case of thinner deposits. 



It now remains to show that the chemical composition of sandy 

 soils is such as we may reasonably expect them to have been formed 

 from the shore sand. 



