JOLL0SOA or INDIA. 



11 



pntra, where they are elevated to 10,(100 feet in the Patkai and 

 Naga Hills. In the Garo Hills this dimislien to 3000 feet, hut they 

 are there in force with a thickness of some 5000-fiOOO feet : vide 

 'Journal Asiatic Society of Bengal,' vol. xsxviii. pt. 2, no. 1, 

 1869, with a Geological Map of a portion of the Khasi Hills 

 near longitude 91° E. 



Connected with this range of the genus, two facts stand out : — 

 (1) The extreme age of the great valleys; (2) the great diiSerence 

 between the MoUuscan fauna of Sikhim and that of the Dafla Hills, 

 still more when it is compared with that of the Arbor country. 

 Tliere are very few species common to both. Few Sikhim species 

 are found in either : all is new, even new genera come in. The 

 reason for this is no doubt due to the physical features of the 

 great valleys : some, such as the Motiass and Subansiri, are very 

 broad ; they go back far into the Range ; their sources glacial, 

 they are separated one from the other by lofty snow-covered 

 longitudinal ranges, which continue high to the plains. They are 

 thus completely isolated one from the other, allowing evolution to 

 go on independently within them and form " specific centres." 



The rich flora and fauna of Sikhim is in direct relationship to 

 its position at the head of the 15ay of Bengal, and for ages has 

 received accessions from that, the Southern side ; so with species 

 of Qhssula, when those at present living between the Teesta and 

 the Monass are compared with those of the Khasi and Garo Hills, 

 100 miles to the south, how small and yet how defined is the 

 difference. 



Himalaya area : P^epresented in the Khasi-Garo area : 



lonciispira. tcnuispirn. 



hastula. sulJiastuJa. 



haeulina. sub-bandina. 



Between these two areas there is an indication of a once more 

 continuous land-surface higher that at present. All this delta area 

 lias gone through considerable depression with denudation. This 

 is so well exemplified by the isolated, weathered masses of intrusive 

 granite rising abruptly out of the alluvium by which they are 

 surrounded at Chanda Dinga, opposite Gwalpara and Doobri. My 

 Survey work took me to the top of several such hills. Granite 

 intrusion is frequently seen ; it is to be noted at Tura and Eiwuk 

 on the Assam Range, and similar intrusions occur further east and 

 north intimately connected with the forces of upheaval. Those near 

 Gwalpara, on the north side of the Brahmaputra, no doubt originally 

 passed up and through stratified rocks long since denuded (perhaps 

 of Cretaceous age) which cover so large an area in the Garo Hills, 

 where they have also suffered great deuudation. 



Numbers, followed by the letters B.M., refer to specimens 

 catalogued in three collecti(m9 presented to the British Museum, 

 viz. those of 1. W. T. Blanfnrd and H. F. Elanford combined, 

 2. Colonel H. Beddome, 3. Godwin-Austen ; they cannot fail 

 to assist those who may study this group or have to name specimens 

 from India. 



