776 Notes, chiefly Geological. [No. 166. 



about twenty-eight miles long from E. to W. It is about twenty- 

 eight miles wide where it opens upon the Malabar coast, and twenty- 

 two at its debouchment on the plains of Coinibatore ; between these 

 points its width is irregular, but it narrows in some parts to eight or 

 nine miles. Its surface, and the lower flank of the Ghauts on each 

 side, are covered with elephant jungle and thickets of bamboo growing 

 in a thick reddish and grey soil, which cover the rocks, and are great 

 obstacles with the jungle to geological examination. Glimpses are 

 occasionally obtained in passing through this forest of the lofty heights 

 of the Nilgherris and Koondas, which flank the right of the Pass, some 

 of which tower 2000 feet above it, and of the mountains, which re- 

 sume the line of elevation on the left. 



The bottom of the Pass is a plain, gradually rising toward the west 

 by rocky undulations running parallel with the line of elevation, 

 which cause alternate rises and falls in its surface. The ascent from 

 Coimbatore and the descent to the sea-coast on the other side are so 

 gentle, that I conceive it probable that the height of the Pass never 

 much exceeds that of Coimbatore itself. 



The boiling point of water makes the town of Palghaut on the 

 Western slope 7-10ths of a degree lower than that of Coimbatore. 

 Down the middle of the Pass winds the Ponani river to the Malabar 

 Coast, and the Indian sea. It is formed by rills from the Ghauts unit- 

 ing in the centre of the Pass west of the water-shed. 



The rocks observed in the Pass, and on its Northern flank, were 

 chiefly of gneiss and hornblende schist, massive hornblende rock, and 

 a small grained quartzy granite, with both black mica and hornblende : 

 the mica is occasionally wanting. 



The mass of gneiss on which the Traveller's Bungalow at Wolioor 

 stands, is of the variety which is termed by geologists granitoidal, or 

 thick-bedded gneiss, and by others, laminar granite. This however 

 though its structure may appear granitic in hand specimens, is evident- 

 ly a stratified rock, and is seen, a few miles westward, to pass into a 

 beautifully characteristic, stratified gneiss, which imbeds small black 

 shining scales of mica, and a granular white quartz in alternate layers. 



A large grained granite penetrates the gneiss, often containing large 

 reddish crystals of foliated felspar, greenish felspar coloured by acty- 

 nolite, and occasionally adularia. 



