On the Structure and Position of Eozoon Ocmadense. 287 



thickness of 1500 feet. These blocks had been brought to 

 the Museum to be sawn into marble; and on being cut 

 through, they were found to be composed of serpentine alter- 

 nating with calc-spar. Thin slices of them having been 

 prepared^ distinct evidence of organic structure was observed 

 in the very first specimen submitted to microscopic examina- 

 tion. The prosecution of the inquiry was confided to that 

 experienced observer, Dr. Dawson, the accomplished Principal 

 of M'Gill College, Montreal ; and under the ■ guidance of the 

 figures and descriptions which I had given of the minute 

 structure of various types of Foraminifera, in the series of 

 Memoirs which had found a place in the Philosophical Trans- 

 actions, and in my general Introduction to the Study of the 

 Foraminifera, published by the Ray Society, he was led to 

 the conclusion that this organism, notwithstanding its com- 

 paratively gigantic dimensions, belongs to the group of Fora- 

 minifera ; being especially related to Polytrema in its zoophytic 

 mode of growth, to Carpenteria in the imperfect separation of 

 the cavity of its shell into distinct chambers, and to Oalcarina 

 in its canal-system. By Dr. Dawson and by Dr. Sterry Hunt 

 it was further shown that the calcareous layers represent the 

 original shell, which in the best preserved Grenville specimens 

 has undergone very little change, but which in the Grand 

 Calumet specimens has become crystalline, whilst in the Bur- 

 gess specimens it has been completely metamorphosed bymag- 

 nesian infiltration. On the other hand, they showed that 

 the siliceous layers represent the original sarcode-body of the 

 animal, which has been replaced by the infiltration of various 

 silicates, as serpentine, pyroxene, and loganite — just as the 

 sarcode -bodies of Foraminifera of various subsequent deposits, 

 from the Silurian to the present time, have been replaced by 

 the infiltration of glauconite and other siliceous minerals ; 

 enabling us to obtain, by the dissolution of their calcareous 

 shells in dilute acids, most perfect models of the soft parts, 

 exhibiting the forms and connections which they possessed in 

 life, with far more truth and completeness than they could be 

 determined by any other method of study.* 



* The existence of such " internal casts" of the shells of Foraminifera — the 

 models of the bodies which occupied them during life — in the Grreensands of 

 various Geological epochs, was first made known by Prof. Ehrenberg. Not 

 long afterwards it was shown by Prof. Bailey, that the Poraminiferal shells of 

 our existing seas are sometimes infiltrated in like manner ; and many beautiful 

 examples of this modelling process have been obtained by Messrs. Parker and 

 Rupert Jones, to whose kindness I owe the "internal cast" of a recent Poly~ 

 stomella, of which I have given a figure in my description of that genus (op. cit.), 

 and which was well designated by my friend Prof. Blanchard as a bijou zoologique. 

 I certainly would not exchange it for a diamond of the same size, since it demon- 

 strated the correctness of my account of the very complex arrangement which I 

 had worked-out, before obtaining it, in the canal-system of the shell of that re- 

 markable genus. 



