2. Other calcareous bodies, probably organic. 3. Objects imbedded in the serpentine. 4. Carbonaceous matters. "(1) The more perfect individuals of Eozoon do not constitute the mass of any of the larger specimens in our collections; but considerable portions of some of them are made up of material of similar minute structure, destitute of lamination, and irregularly arranged. Some of this material gives the impression that there may have been organisms similar to Eozoon, but growing in an irregular or acervuline manner without lamination. Of this, however, I cannot be certain; and, on the other hand, there is distinct evidence of the aggregation of fragments of Eozoon in some of these specimens. In some they constitute the greater part of the mass. In others they are imbedded in calcareous matter of a different character, or in serpentine or granular pyroxene. In most of the specimens the cells of the fossils are more or less filled with these minerals; and in some instances it would appear that the calcareous matter of fragments of Eozoon has been in part replaced by serpentine." [I may add here that in the limestone at Côte St. Pierre there are in some of the beds successive laminæ with grains of serpentine and others with crystals of dolomite, and that both contain fragments of Eozoon. It thus seems as if the magnesia associated with the limestone, at some stages of deposition took the form of silicate, and in others that of carbonate. I may also observe here that I have detected fragments of Eozoon in Laurentian limestone from New Brunswick, from Chelmsford in Massachusetts, from Warren County, New York, from Brazil, and from the Alps.] "(2) Intermixed with the fragments of Eozoon above referred to are other calcareous matters apparently fragmentary. They are of various angular and rounded forms, and present several kinds of structure. The most frequent of these is a strong lamination varying in direction according to the position of the fragments, but corresponding, as far as can be ascertained, with the diagonal of the rhombohedral cleavage. This structure, though crystalline, is highly characteristic of crinoidal remains when preserved in altered limestones. The more dense parts of Eozoon, destitute of tubuli, also sometimes show this structure, though less distinctly. Other fragments are compact and structureless, or show only a fine granular appearance; and these sometimes include grains, patches, or fibres of graphite. In Cambro-Silurian limestones, fragments of corals and shells which have been partially infiltrated with bituminous matter, show a structure like this. On comparison with altered organic limestones of the Cambro-Silurian system, these appearances would indicate that, in addition to the debris of Eozoon, other calcareous structures, more like those of crinoids, corals, and shells, have contributed to the formation of the Laurentian limestones.