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Show 42 THE PAST CONDITION you for the purpose of raising a paradoxical difficulty; the fact is, that the great mass of deposits have taken place in sea-bottoms which are gradually sinking, and have been formed under the very conditions I am here suppos1ng. Do not run away with the notion that this subverts the principle I laid down at first. The error lies in extending a principle which is perfectly applicable to deposits in the same vertical line to deposits which are not in that relation to one another. It is in consequence of circumstances of this kind, and of others that I might mention to you, that our conclusions on and interpretations of the record are really and strictly only valid so long as we confine ourselves to one vertical section. I do not mean to tell you that there are no qualifying circumstances, so that, even in very considerable areas, we may safely speak of conformably superimposed beds being older or younger than others at many different points. But we can never be quite sure in coming to that conclusion, and especially we cannot be sure if there is any break in their continuity, or any very great distance between the points to be compared. Well now, so much for the record itself,-so much for its imperfections,-so much for the conditions to be observed in interpreting it, and its chronological indications, the moment we pass beyond the limits of a vertical linear section. Now let us pass from the record to that which it contains,-from the book itself to the writing and the figures on its pages. This writing and these figures consist of remains of animals and plants which, in the OF ORGAXIC NATURE. 43 great majority of cases, have lived and died in the very spot in which we now find them, or at least in the immediate vicinity. You must all of you be a·wareand I referred to the fact in last l\1onday's lecturethat there are vast numbers of creatures livinO' at the b bottom of the sea. These creatures like all others ' ' sooner or later die, and their shells and hard parts lie at the bottom; apd then the fine mud which is being constantly brought down by rivers and the action of the wear and tear of the sea, covers them over and protects them from any further change or alteration; and, of course, as in process of time the mud becomes hardened and solidified, the shells of these animals are preserved and firmly em bedded in the limestone or sandstone which is being thus formed. You may see in the galleries of the n1useum upstairs specimens of limestones in which such fossil remains of existing animals are embedded. There arc some specimens in which turtles' eggs have been imbedded in calcareous sand, and before the sun had hatched the young turtles, they became covered over with c:.tlcareous mud, and thus have been preserved and fossilized. Not only does this process of imbedding and fossilization occur with marine and other aquatic animals and plants, but it affects those land animals and plants which are drifted away to sea, or become buried in bogs or morasses; and the animals which have been trodden down by their fellows and crushed in the n1ud at the river·'s bank, as the herd have come to drink. In any of these cases, the organisms may be crushed or be mutilated, before or after putrefaction, in such a manner that perhaps only a part will be left |