Thompson was therefore instructed to proceed to Lake la Biche or Red Deer lake, whose waters fall into the Athabaska river about fifty miles below Athabaska Landing. On the 14th of July, he set forth from Grand Portage with the Churchill river brigade. By the middle of August they had reached Cumberland House, and a week later they had crossed over Frog Portage to the main stream of the Churchill. From this point west the route lay through a region as yet new to Thompson. As he ascended the river to Isle à la Crosse, he found that the country was still composed of the denuded rock with which he was familiar on the lower stretches of the river. Ridges of this rock, crossing the valley of the stream from point to point, gave it the character of an irregular chain of lakes with many portages and falls. Like the rest of the stony country, it was somewhat poor in game and fur-bearing animals, although many of the lakes teemed with fish. From Isle à la Crosse to the valley of the Athabaska there were two possible routes. To the north there was Turnor's old course by way of Methy Portage and Clearwater river. To the south, the Beaver river led through a district of plain and forest to its headwaters at Beaver lake, from which there was an easy portage over the height of land to Lake la Biche. Thompson followed the Beaver river, and arrived at Lake la Biche in time to build a post before the beginning of winter. He was now at the southern end of that vast stretch of country which he calls the Great Western Forest, and almost in the same latitude as that of Reed lake in the Muskrat country where he had spent the winter of 1794-5. He was thus in a position to compare the climate and soil of this region with that of his old home on the eastern or "Siberian" side of North America. Throughout the long winter months, he kept as usual a careful record of the temperatures registered from day to day by his thermometer. At Reed lake, the temperature for December had varied from +31° to -45° with a mean of -10° F. For January it had varied from +11° to -47° with a mean of -21.3°, and for February from +39° to -31° with a mean of +6°. At Lake la Biche he found that although in each of the three winter months, the mercury sank as low as 48° below zero, it rose at times as high as 43° above, and that the mean for December, the coldest month, was not lower than -6.5°. Then, too, while Reed lake was hardly above the level of Hudson Bay, the country about Lake la Biche was high and dry, and the snow did not lie so thick on the ground at the end of winter. Accordingly, the rays of the sun had a chance to exert their power on the face of the land much earlier in the year, and spring burst at Lake la Biche long before winter had loosened his iron grip on the region about Reed lake.