CHIN HILLS, a constituent hill-group of the mountain arc, stretching from the Arakan Yoma northwards to the Patkai hills, between Burma and India. This mountain arc, compressed at either end, has advanced farthest towards the west in the centre where the long parallel folds are most numerous and the arc broadest. The Chin hills form the highest part of this central stretch. They consist simply of a succession of long narrow troughs and ridges, from 5,000 to 9,00o ft. high, with little flat land either in the valley bottoms or on the ridge tops. There is a marked climatic contrast between the humid tropical conditions of the deeply cut valleys and the cooler temperatures of the ridges. This contrast is reflected in the vegetation. Above 3,00o ft. the tropical forest gives way to oak and pine woods which in turn give way above 7,000 ft. to the rhododendron. A migratory form of agriculture, the taungya system, is practised in these hillside woods where the greater part of the population is centred. Clear ings are made and the wood burnt for fertilizer. Such clearings are cultivated for two or three years and then abandoned. Bam boo, bracken and elephant grass then spring up with such vigour that natural re-afforestation is impossible. The main crop culti vated by this method is jowar millet contrasting with rice in the plains of Lower Burma. Some rice is, however, grown in the Chin hills on the lower slopes on terraces constructed with the help of felled timber.
The north-south trend lines of Indo-China as a whole have permitted the flooding of the region with "Mongoloid" peoples coming down from the north and have hindered east-west move ment of both peoples and culture. The Arakan Yoma-Patkai mountain arc, of which the Chin hills form a part, exemplifies these features. It constitutes a frontier zone between Indian and Burmese cultures and its bill-tribes remained independent of British administration until the close of the 19th century. The Chin hills, lying on the Irrawaddy side of the watershed, were eventually occupied to prevent the raids by hill-folk on the plains of Burma. They are now administered primarily with the object of preserving the peace and of building up a sound government on the basis of the tribal system. The substitution of peaceful agri culture for raiding is producing changes in the distribution of population; the defensive hill-sites are being deserted and popula tion is becoming concentrated on the more easily cultivable land. The whole of the southern part of the Arakan Yoma-Patkai moun tain arc from the Chin hills southward into the Arakan Yoma is occupied by the Chin peoples who belong to the Southern Mongo loid race group and are linguistically a branch of the Tibeto Burmans. The Chin hills proper are occupied by only the northern tribes of the Chin peoples. At the time of the 1921 Census the population of the Chin hills was 110,079. (P. M. R.)