Th: Jefferson returns his thanks to mr Schoolcraft for the Memorial he has been so kind as to send him on the fossil tree of the river des Plaines. it is a valuable element towards the knolege we wish to obtain of the crust of the globe we inhabit: and it’s crust alone is immediately interesting to us. we are only to guard against drawing our conclusions deeper than we dig.   Mr Schoolcraft is entitled to the thanks of the lovers of science for the preservation of this fact. he has those of Th: J. with his salutations of esteem and respect.