Carpenter, and represented in specimens in my collection presented by him, was evidently of the same type with that preserved in the canals of these ancient fossils. Fig. 10 is an accurate representation of the first seen group of canals penetrated by serpentine. [Illustration: Fig. 8. _Weathered Specimen of Eozoon from the Calumet._ (Collected by Mr. McMullen.)] [Illustration: Fig. 9. _Cross Section of the Specimen represented in Fig. 8._ The dark parts are the laminæ of calcareous matter converging to the outer surface.] On showing the structures discovered to Sir William Logan, he entered into the matter with enthusiasm, and had a great number of slices and afterwards of decalcified specimens prepared, which were placed in my hands for examination. Feeling that the discovery was most important, but that it would be met with determined scepticism by a great many geologists, I was not content with examining the typical specimens of Eozoon, but had slices prepared of every variety of Laurentian limestone, of altered limestones from the Primordial and Silurian, and of serpentine marbles of all the varieties furnished by our collections. These were examined with ordinary and polarized light, and with every variety of illumination. Dr. Hunt, on his part, undertook the chemical investigation of the various associated minerals. An extensive series of notes and camera tracings were made of all the appearances observed; and of some of the more important structures beautiful drawings were executed by the late Mr. H. S. Smith, the then palæontological draughtsman of the Survey. The result of the whole investigation was a firm conviction that the structure was organic and foraminiferal, and that it could be distinguished from any merely mineral or crystalline forms occurring in these or other limestones. [Illustration: Fig. 10. _Group of Canals in the Supplemental Skeleton of Eozoon._ Taken from the specimen in which they were first recognised. Magnified.]