"When we visited the spot, the water of the river was at the lowest stage; but there was no part of the tree within some inches of the surface. The rocky bed of the stream was formed round and upon it. We raised from it pieces of the rock, which were evidently in situ, and which had been formed upon the tree posterior to the period of its deposit in its present situation. This rock is a species of sandstone, whose characteristic features must be well known to you.
"There are no mineralized substances of vegetable origin in the vicinity of this specimen, nor are there any appearances which indicate that its present condition has been caused by any peculiar property in the waters of the Des Plaines."
ADDENDA.
The publication of the foregoing memoir led to several letters being addressed to the author on topics connected with it. Some of these were from gentlemen eminent in science or politics, whose opinions are entitled to the highest respect. Extracts are given from such only as introduce new data, either of fact or opinion.
Geological Theories.—Professor Dewey, of Williams College, observes: "A friend has just lent me your 'Memoir on a Fossil-Tree.' Though the account is very interesting, I do not perceive its exact bearing on the Neptunian and Plutonian hypotheses. The fault is doubtless in me, and you will excuse my remarks and set me right. I had supposed the Huttonians and Wernerians did not dispute about the manner in which the secondary rocks were formed. Macculloch, and others before him, led me into this opinion, though it may be erroneous. But Bakewell, who is referred to as authority in Rees's Cyclopædia, says, p. 131: 'Geologists are agreed that secondary rocks have been formed by the agency of water.' If this be so, they would agree generally with the account of Dr. Cooper respecting the formation of petrifactions, and especially those of vegetables, and the fossil-tree would be treated of in a similar manner by both."
Hutton's original hypothesis, and not the modifications of it introduced by the Neptu-Vulcanists, were adverted to in reply. Subsequently, Professor Dewey writes:—
"I was greatly obliged by your letter in various respects, and I write you now to make my acknowledgments for it, as well as to maintain the correctness of your notions on the Huttonian hypothesis. As you had seen a Scotch mineralogist directly from the mint of Playfair, I had every reason to suppose you had received correct views of Playfair's notions on the subject. I have been led, therefore, to examine the matter, and, as I may have set you on the search, I wish to prevent your continuing it on my account, or from what I wrote.
"Playfair's Illustrations I have never seen. Occasional extracts, or allusions to its points, have fallen in my way. But I have before me a very full abstract of Hutton's paper on the subject, from the Transactions of the Royal Society of Edinburgh. It is from the very paper in which he announces his hypothesis. In that paper he mentions that the consolidation of all the hard crust of the globe has been effected by heat and fusion, extending it to secondary as well as primitive rocks, and mentioning particularly Spanish marble, shell limestone, oolite, and chalk.
"This operation of heat, he says, is exemplified by chalk, which is to be found in all gradations, from marble to loose chalk. This is his precise notion, but not his words. I had once looked at this paper before, and thought much of this theory; but this thought had been obliterated from my mind by thoughts advanced by others, as I thought in consistency with the sentence I quoted from Bakewell. At least, one objection to Hutton's views would be removed by modifying his theory in the manner it seems to be by Bakewell. Though Hutton does not think this to be necessary; for he appears to feel no difficulty in accounting for petrifactions of wood on his hypothesis, for he mentions that we have many proofs of the penetration of flinty matter, in a state of fusion, in other bodies, such as insulated pieces of flint in chalk or sand, and fossil wood penetrated with silicious matter.