Life's Dawn on Earth / Being the history of the oldest known fossil remains, and their relations to geological time and to the development of the animal kingdom

by Sir John William Dawson

Eozoon Canadense, Dawson.

In rounded masses or thick encrusting sheets, frequently of large dimensions. Typical structure stromatoporoid, or with concentric calcareous walls, frequently uniting with each other, and separating flat chambers, more or less mammillated, and spreading into horizontal lobes and small chamberlets; chambers often confluent and crossed by irregular calcareous pillars connecting the opposite walls. Upper part often composed of acervuline chambers of rounded forms. Proper wall tubulated very finely. Intermediate skeleton largely developed, especially at the lower part, and traversed by large canals, often with smaller canals in their interstices. Lower laminæ and chambers often three millimetres in thickness. Upper laminæ and chambers one millimetre or less. Age Laurentian and perhaps Huronian.

Var. MINOR.—Supplemental skeleton wanting, except near the base, and with very fine canals. Laminæ of sarcode much mammillated, thin, and separated by very thin walls. Probably a depauperated variety.

Var. ACERVULINA.—In oval or rounded masses, wholly acervuline. Cells rounded; intermediate skeleton absent or much reduced; cell-walls tubulated. This may be a distinct species, but it closely resembles the acervuline parts of the ordinary form.

Eozoon Bavaricum, Gümbel.

Composed of small acervuline chambers, separated by contorted walls, and associated with broad plate-like chambers below. Large canals in the thicker parts of the intermediate skeleton. Differs from E. Canadense in its smaller and more contorted chambers. Age probably Huronian.

Genus ARCHÆOSPHERINA.

A provisional genus, to include rounded solitary chambers, or globigerine assemblages of such chambers, with the cell-wall surrounding them tubulated as in Eozoon. They may be distinct organisms, or gemmæ or detached fragments of Eozoon. Some of them much resemble the bodies figured by Dr. Carpenter, as gemmæ or ova and primitive chambers of Orbitolites. They are very abundant on some of the strata surfaces of the limestone at Côte St. Pierre. Age Lower Laurentian.