1845.] Geological Notes of Southern India. 399 



caused by the currents of air on their surface resemble those caused 

 by currents of water, and the N. and S. direction of their major 

 axis shows the Easterly and Westerly course of the late or existing 

 prevalent winds. Their Eastern sides have a sloping direction ; fall- 

 ing off rather abruptly to the West at about an angle of 45°, indica- 

 ting that the wind which raised them h\ewfrom the E. On the surface 

 were scattered here and there shells and fragments of shells blown 

 up from the beach. The footsteps of waders, and other aquatic birds 

 could be occasionally tracked where the wind had not again covered 

 them up with loose sand. 



These, together with the ripple marks, marine shells, and the 

 elevation of these moving sands, form an interesting example of the 

 manner in which strata of aqueous sub-marine origin may be imitat- 

 ed by the simple action of the wind on loose sand. Consolidation, 

 and a more distinct stratification alone are wanting to convert these 

 heaps into a fossiliferous ridge. The sand is often bound together by 

 the long interlaced roots of grasses, &c. 



Calorific action of sun's rays on surface of Sand Dunes. At 5 

 p. m. sky clear, slight breeze just perceptible; the thermometer placed 

 on the sand and freely exposed to the sun's rays indicated a heat of 

 100° 3'. Simply suspended in the air, about 12 feet above the surface 

 of the sand, equally exposed to the sun's rays, it stood at J8° 5'. 



Nocturnal Radiation from surface of Sand Dunes. The radiating 

 powers of the sand dunes are considerable. At 3 a. m., night nearly 

 calm, sky clear, the thermometer shaded from radiation, and placed 

 on a table about four feet from the ground, stood at 67°. Placed on the 

 grass and freely exposed bulb thinly covered with a little white wool, 

 it fell to 65.5°. But on the surface of the sand dunes it fell to 62°. 

 The sand is fine and quartzy. 



As serial stillness is one of the conditions necessary to the full re- 

 frigerating effects of radiation, it is likely that on the coast, which is 

 hardly ever free from currents, however slight, resulting from the 

 regular alternations of the land and sea breezes, the differences of 

 temperature obtained by radiation will hardly ever be so great as the 

 table-lands of India. The lulls between the land and sea breezes 

 perhaps present the most eligible times for such experiments, 



The temperature of the water of the wells is not far from what may 

 be the mean average temperature of the place, viz., from 80° 2' to 81°. 



