10 GEOLOGY OF TRICHINOPOLY, &C. [ClIAP. I. 



the coast and up to the foot of the Kalroyen mountains and the 



Patchamullays, the greater part of the water supply is obtained from 



the north-east monsoon, which always gives rise to heavy freshets in 



the Vellaur and Punniar rivers. The great freshets of the Cauvery, 



however, depend upon the bursting of the south-west monsoon on the 



western ghats, where this great river takes its rise. By these freshets, 



which generally occur in June or July, the river is completely filled 



and not unfrequently it inundates the low country of the delta to a 



very great extent. On account of its proximity to the great Palghat 



„ „ 1 I. i. Pass, the influence of the south-west monsoon is 

 Influence of Palghat ' 



^^P* much greater over the country we are dealing 



with, than over the regions both further north and further south. 

 The south-west wind blows with great force into the Palghat Pass, 

 which has a width of about 25 miles, diminishes a little as the moun- 

 tains recede, and forms a funnel mouth out of which the wind issues. 

 Afterwards it meets with little or nothing in the Coimbatore district to 

 oppose it, till east of the Cauvery, the Shevaroys and Kolymullays 

 break its force, and receive in heavy showers a large share of the mois- 

 ture then remaining. A very strong current is almost without intermis- 

 sion urged through the Salem-Ahtoor valley as long as the south-west mon- 

 soon remains in force on the western coast. A similar and equally strong 

 wind blows through that valley from the opposite quarter during the 

 strength of the north-east monsoon. Southward of the Kolymullays no 

 obstruction is offered to the westerly wind, owing to the absence of moun- 

 tains, (the nearest being the Dindigal mountains, at a distance of some 

 40 miles,) and in consequence it blows very strongly across the delta 

 to the east coast.^ This easterly wind, added to the evaporation 



* To the effects of this violent rush of wind from the Palghat Pass across the very 

 dry Coimbatore district, Colonel Lambton, in his " Report on the Trigonometrical survey of 

 the southern division," ascribes the formation of a rather extensive series of blown sand- 



( 232 ) 



