our situation hazardous from the sliding in of the bank around, and which might easily have involved us in difficulty. By the time we had proceeded about a mile and a half along the bend or right hand channel of 67 and 68, which lie opposite to each other, a fog sprung up, so very dense as to render our situation amidst almost unseen obstacles extremely dangerous. We had no alternative but rowing over to the bar of the island on our left, in which attempt we at length succeeded, not, however, without a risk of grounding. Here we lay until towards evening, when we proceeded to the termination of the 68th island, and made an indifferent landing. On exposing the thermometer to the air, it rose and remained at 62°. In the water it fell to 42°; the difference being 20°, which readily accounted for the dense fog that exclusively enveloped the river. This coldness of the water was no doubt occasioned by the thawing of ice in the upper part of the river, or some of its more considerable tributary streams, in consequence of which, the vapours of the moist and warm air were perpetually precipitated over it. The air, of unequal temperature, now and then felt extremely warm.
On the 11th we were again detained by the fog and heavy rain, but turned out about 10 o'clock. After proceeding opposite the commencement of the 69th island we stopped in consequence of the fog. Here, on ascending the bank, I found the woods almost impenetrably laced with green briars (Smilax), {63} supple-jacks (Œnoplia volubilis), and the Brunichia, and for the first time recognised the short-podded honey-locust (Gleditscia brachycarpa), a distinct species, intermediate with the common kind (G. triacanthos), and the one-seeded locust (G. monosperma), differing from G. triacanthos in the per-
