Coprolites (Gr. dung, and a stone), the fossil excrements of various kinds of fishes and saurians, first recognized as such by Buckland. They are found, sometimes in enormous quantities, in several geological formations, as the tertiary, chalk, oolite, lias, and carboniferous, scattered among the other fossils in these rocks, and sometimes met with enclosed among the ribs of the fossilized ichthyosauri. They occur to some extent in this country in the greensand and coal formations, but in England most abundantly in the lias. They vary greatly in size, some being the product of the largest ichthyosauri, and containing within them scales and bones of fishes and other animals which served as food to these monsters; while some belonged to smaller individuals, and are now seen in stony lumps of only an inch or two in length. Their color is whitish, grayish, and from this to black. On their surface are still impressed the marks of the tortuous wrinkles of the intestines. The animal remains preserved in the coprolites indicate the prey of these fishes and saurians.

The larger kinds appear to have fed upon the smaller of their own species; and these, from the bones found in the coprolites of the largest ichthyosauri, could not have been less than 7 ft. in length. A remarkable instance is given by Dr. Buckland of the minute accuracy with which the principles of comparative anatomy are applied to investigations of this nature. A small scale of a fish seen upon one side of a coprolite was shown to Prof. Agassiz, who at once recognized it as belonging to the extinct species pholidophorus limbatus; and from a minute tube upon its inner surface, hardly discernible without a microscope, he observed that it must have been on the left side of the body near the head. This tube passed through the scales from the head to the tail of the fish, conveying a lubricating mucus. - Different coprolites differ considerably in chemical composition; those containing much phosphate of lime are very valuable as fertilizers, and are used as such. In the following table the first and fourth columns of figures give the composition of the coprolites of the coast of Suffolk; the second column, those found in the ironstone of Burdiehouse in Scotland; the third, those found in the limestone of Burdiehouse, according to A. Connel; the fifth, those over the lias near Stuttgart, Germany; the sixth, those from Bohemia:

* Quartz mills.

The varying chemical composition of this mineral is to be expected from its origin; the form and color also differ greatly, but the specific gravity is always between 2.6 and 2.8.