182 DR. D. LYALL ON THE BOTANY 
Pend Oreille valley, we have an under-vegetation resembling in 
many of its features that of the Lower Fraser ; whilst the produc- 
tions of the Similkameen valley and the Tobacco Plains, and part 
of the Flathead valley, approximate to those of the dry region of 
the Columbia. 
Such of the intervening mountain-ranges as we had an oppor- 
tunity of examining afford specimens of alpine plants the same as 
were obtained on the Cascades and Rocky Mountains. 
With reference to the first district, it may be mentioned that 
the line of separation between Washington Territory and British 
Columbia for the first twenty-five miles from the sea runs nearly 
parallel to the Fraser River, and at an average distance of less 
than ten miles from it. About twenty-four miles inland it strikes 
one of the spurs of the Cascades. Up to this point the ground is 
nearly level, but little above the sea, and densely timbered with 
trees mentioned below. 
The Lower Fraser River has along its left or south bank a 
range of low rocky hills, extending from Langley to the mouth 
of the Sumass River; and to the southward of these, between 
them and the spur of the Cascades just mentioned, lies the Sumass 
prairie. Nearly in the middle of this prairie is the lake of the 
same name, about ten miles long by four broad at its widest part. 
During the season of flood it extends from hill-foot to hill-foot, 
and even after the subsidence of the waters its mud-banks or 
beaches reach certain points on both sides. 
The larger half of the prairie is at the south-west end of the 
lake, and is (roughly) about four miles square. 
The prairie-ground at the north-east end of the lake is bounded 
by a belt of trees separating it from the clear or prairie ground on 
the banks of the Chilukweyuk River. The clear ground on both 
sides of this river has been apparently formed partly by the re- 
peated action of fires, destroying the trees which at one time grew 
on the higher banks, and partly by the action of the annual floods 
which overflow a large portion of it. 
Most of the collections made in the first district were from the 
Sumass and Chilukweyuk prairies and from the comparatively low 
adjoining hills. 
These (so-called) prairies have, during the season of flood, more 
the appearance of immense lakes, being, with the exception of à 
higher ridge here and there, almost entirely covered by water. 
As soon as this retreats, the heat of the sun in July and August 
causes the Grasses and Cyperacex to grow with extraordinary lux- 
