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

4th. This overlooks the filling of chamber casts with pyroxene, dolomite, or limestone. Even in the case of loganite this objection is of no value unless it can be applied equally to the similar silicates which fill cavities of fossils[AQ] in the Silurian limestones and in the green-sand.

[AQ] See for a full discussion of this subject Dr. Hunt’s “Papers” above referred to.

5th. Dr. Gümbel’s observations are those of a highly skilled and accurate observer. Even if crystalline forms appear in “chamber casts,” this is as likely to be a result of the injury of organic structures by crystallization, as of the partial effacement of crystals by other actions. Crystalline faces occur abundantly in many undoubted fossil woods and corals; and crystals not unfrequently cross and interfere with the structures in such specimens.

6th. On the contrary, the Canadian specimens prove clearly that the veins of chrysotile have been filled subsequently to the existence of Eozoon in its present state, and that there is no connection whatever between them and the Nummuline wall.

7th. This I have never seen in all my examinations of Eozoon. The writers must have mistaken veins of fibrous serpentine for the nummuline wall.

8th. Only if such grains of chondrodite are themselves casts of foraminiferal chambers. But Messrs. King and Rowney have repeatedly figured mere groups of crystals as examples of the nummuline wall.

9th. Dr. Carpenter has shown that this objection depends on a misconception of the structure of modern Foraminifera, which show similar appearances.

10th. That disseminated crystals occur in the Eozoon limestones is a familiar fact, and one paralleled in many other more or less altered organic limestones. Foreign bodies also occur in the chambers filled with loganite and other minerals; but these need not any more be confounded with the pillars and walls connecting the laminæ than the sand filling a dead coral with its lamellæ. Further, it is well known that foreign bodies are often contained both in the testa and chambers even of recent Foraminifera.

11th. The canal system is not always filled with serpentine or malacolite; and when filled with pyroxene, dolomite, or calcite, the forms are the same. The irregularities spoken of are perhaps more manifest in the serpentine specimens, because this mineral has in places encroached on or partially replaced the calcite walls.