The big movement of the fall migration finally began to materialize on Sunday, August 24. This and the next few days were filled with memorable experiences. The throngs of Caribou passing at such times around the head of Windy Bay and across the lowermost portions of Little and Windy rivers may be accounted for, in part, by the local topography (map 1). The upper part of Windy Bay, occupied by numerous islands of various sizes and extending about 5 miles in an east-west direction, opposes something of a barrier to the Caribou in their southward trek. The easiest way to overcome this barrier is to by-pass it. So the migrant herds approaching the north shore of the bay turn westward toward Little River. At a point half a mile short of this stream a rather minor proportion of the Caribou actually do essay a passage of Windy Bay. They cross an island lying very close to the north shore, then steer for a small rocky islet a quarter of a mile northwest of the mouth of South Bay. Here they get a brief respite from swimming by walking through the shallow bordering waters, then continue straight on to the rugged south shore of Windy Bay. This course is roughly parallel to, and a quarter of a mile west of, the one pursued northward or northeastward across the ice in the spring migration. The Caribou were seen to follow this water route on various days from August 24 to September 8, and again on October 7. Like the one across the ice, it is probably a regular, well-established, annual route. The greater number of the migrants proceed along the north shore of the bay to Little River and are there confronted with a choice of various further routes. Some continue for an indefinite distance up the northeastern bank, passing Lake Charles on their right, though other animals, coming from the north, may be following this bank in the opposite direction. Probably most of the Caribou arriving from the eastward either plunge into Little River at its mouth and swim across (figs. 9, 10, 12) or pass upstream for a bare quarter of a mile and then wade across at a rapid (figs. 7, 8).