[Footnote 21:  More extensive observations than what Cook’s time allowed him to make, would be requisite to determine the questions which he has just now started.  Besides, it is fair to remark, that there is some reason for demurring at one of the premises, with which he sets out, viz. that the islands, he speaks of, are as well situate for receiving seeds, as any of the coasts are that abound in wood.  At least, before admitting it, we ought to be assured of the equal vicinity of sources from which these seeds might be received, the predominance or occasional alteration of currents fit for their conveyance, &c.  On the other hand, what is conjectured about the variety of soils, is so obvious, as to need no pointing out.  With respect to the drift-wood, it may be right to state, by way of corroborating a supposition hazarded by Cook, that there is reason to believe, that much of the internal parts of North America, and even the declivities, though not the summits of most of the high ranges of mountains traversing it, either have been, or are, well covered with trees.  Here, it is worth while to allude to a very singular circumstance mentioned in the account of Lewis and Clarke’s Travels to the Source of the Missouri, &c. viz. that a great number of the trunks of trees of the pine genus were found standing erect, and with their roots fixed, but in a state of decay, in the bottom of the Columbia river, on the west coast.  It is difficult to explain this, but on the supposition of some considerable change in the course of the river; and it is sufficiently obvious, that such changes, which we know have often occurred elsewhere, might soon occasion the removal of trees from their original situation to any distance.  We cannot spare time or room to carry on the investigation of the subject; but no reader can be at a loss to estimate the probable results of the fact now mentioned.  To some persons, however, it may be necessary to mention, that the Missouri itself is a striking instance of both changeability of course, and a corresponding operation in transporting trees, &c.; the latter circumstance being apparently both the cause and the effect of the former.  Thus we are informed in the work already referred to, that at the place where the party embarked on the last-mentioned river, its current, which was extremely rapid, brought down great quantities of drift-wood, that its bottom was full of logs of trees, and that the course of the water was frequently varying from the effects of sand-bars, &c. of its own formation.  For an obvious reason, it is to be wished, that Cook had mentioned to what species of trees the drift-wood he found had belonged.  How rarely are even intelligent persons quite aware of the importance of the facts which are presented to them; and how much has been lost, or which is, in fact, the same thing, not gained to science, in consequence of the carelessness with which they have been examined!—­E.]