518 FORAMINIFEBA. : — EOZOON CANADENSE. 



growth over vast areas of the Sea-bottom in the Laurentian 

 epoch.* 



397. Whilst essentially belonging to the Nummuline group, in 

 virtue of the fine tubulation of the Shelly layers forming the 

 ' proper wall ' of its chambers, Eozoon is related to various 

 types of recent Foraminifera in its other characters. For in its 

 indeterminate Zoophytic mode of Growth it agrees with Potytrema 

 (§ 386) ; in the incomplete separation of its Chambers it has its 

 parallel in Carpenteria (§ 384) ; whilst in the high development 

 of its Intermediate Skeleton and of the Canal system by which this 

 is nourished, it finds its nearest representative in Calcarina 

 (§ 387). Its Calcareous layers were so superposed, one upon 

 another, as to include between them a succession of ' storeys' of 

 Chamber's (Plate xvn., fig. 1, a 1 , a ', a 2 , a 2 ) ; the Chambers of 

 each 'storey' usually opening one into another, as at a, a, like 

 Apartments en suite ; but being occasionally divided by complete 

 Septa, as at b, b. These Septa are traversed by passages of com- 

 munication between the chambers which they separate ; resembling 

 those which, in existing types, are occupied by stolons connecting 

 together the segments of the Sarcode-body. Each layer of Shell 

 consists of two finely-tubulated or ' Nummuline ' lamellae, b, b, 

 which form the boundaries of the chambers beneath and above, 

 serving (so to speak) as the ceiling of the former, and as the floor 

 of the latter ; and of an intervening deposit of homogeneous Shell 

 substance, c, c, which constitutes the 'Intermediate Skeleton.' 

 The thickness of this interposed layer varies considerably in 

 different parts of the same mass ; being in general greatest near 

 its base, and progressively diminishing towards its upper surface. 

 The 'intermediate skeleton' is occasionally traversed by large 

 passages (d), which seem to establish a connection between the 

 successive layers of Chambers ; and it is penetrated by arborescent 

 systems of Canals (e, e), which are often distributed both so ex- 

 tensively and so minutely through its substance, as to leave very 

 little of it without a branch. 



398. Now in the Fossilized condition in which Eozoon is most 

 commonly found, not only the cavities of the Chambers, but the 

 Canal-systems to their smallest ramifications, are filled up by the 

 Siliceous infiltration which has taken the place of the original 

 Sarcode-body, as in the cases already cited (§ 390, note) ; and thus 

 when a piece of this fossil is subjected to the action of dilute Acid, 

 by which its Calcareous portion is dissolved away, we obtain an 

 Internal Cast of its Chambers and Canal-system (Plate xvn., 

 fig. 2), which, though altogether dissimilar in arrangement, is 

 essentially analogous in character to the 'internal casts' re- 



* For a fuller account of the results of the Author's own Study of Eo- 

 zoon, and of the basis on which the, above reconstruction is founded, see 

 his Papers in "Quart. Journ. of Geol. Soc," Vol. xxi., p. 59, and Vol. xxii., 

 p. 219 ; and in the "Intellectual Observer, " Vol. vii. (1865), p. 278. 



