We found the branches of these trees and the ground underneath strewed over with a white substance resembling small flakes of snow, called by the colonists manna. I am aware that an erroneous idea exists that this matter is deposited by the locusts; but in fact it is an exudation from the Eucalyptus; and although I saw it beneath another kind of tree, it must have been carried there by the wind. A different sort, of a pale yellow colour, is found on a smaller species of Eucalyptus growing on highlands, and is much sought after for food by the natives, who sometimes scrape from the tree as much as a pound in a quarter of an hour. It has the taste of a delicious sweetmeat, with an almond flavour, and is so luscious that much cannot be eaten of it. This is well worthy of attention from our confectioners at home, and it may hereafter form an article of commerce, although from what has fallen under my own observation, and from what I have learnt from Mr. Eyre and others, I should say it is not of frequent occurrence. The first kind, being found strewed underneath the tree probably exudes from the leaf, whilst the second oozes from the stem. The wood of the latter is much used for fuel by the natives, especially in night-fishing, and burns brightly, without smoke, diffusing also a delicious aromatic smell. HOBSON'S BAY. On Christmas day, which we spent in Hobson's Bay, we experienced one of those hot winds which occasionally occur coming off the land. During its prevalence, everything assumes a strange appearance--objects are seen with difficulty, and acquire a tremulous motion like that which is imparted to everything seen through the air escaping from an over-heated stove. The thermometer on a wall under the glare of the sun, stood at 135 degrees. We surveyed Hobson's Bay during our stay, and connected it by triangulation with Melbourne. Our observations were made at the inner end of a small jetty. The mouth of the Yarra-yarra is closed up by a bar, which from its soft muddy nature may be easily removed. The deepest water we found on it at high tide was nine feet. CORIO HARBOUR.