1865.] DAWSON — STRUCTURE OF EOZOoN. 103 



cleavage, their forms and structures have no relation to this. Their 

 cells and canals are rounded, and have smooth walls, which are 

 occasionally lined with films apparently of carbonaceous matter. 

 Above all, the minute tubuli are different from anything likely to 

 occur in merely crystalline calc-spar. While in such rocks little 

 importance might be attached to external forms simulating the 

 appearances of corals, sponges, or other organisms, these delicate 

 internal structures have a much higher claim to attention. Nor is 

 there any improbability in the preservation of such minute parts 

 in rocks so highly crystalline, since it is a circumstance of frequent 

 occurrence in the microscopic examination of fossils that the finest 

 structures are visible in specimens in which the general form and 

 the arrangement of parts have been entirely obliterated. It is also 

 to be observed that the structure of the calcareous laminae is the 

 same, whether the intervening spaces are filled with serpentine or 

 with pyroxene. 



3. The structures above described are not merely definite and 

 uniform, but they are of a kind proper to animal organisms, and 

 more especially to one particular type of animal life, as likely as 

 any other to occur under such circumstances ; I refer to that of 

 the Rhizopods of the order Foraminifera. The most important 

 point of difference is in the great size and compact habit of growth 

 of the specimens in question ; but there seems no good reason to 

 maintain that Foraminifera must necessarily be of small size, more 

 especially since forms of considerable magnitude referred to this 

 type are known in the Lower Silurian. Prof. Hall has described 

 specimens of Eeceptaculites twelve inches in diameter ; and the 

 fossils from the Potsdam formation of Labrador, referred by Mr. 

 Billings to the genus Archoeoci/athus, are examples of Protozoa with 

 calcareous skeletons scarcely inferior in their massive style of 

 growth to the forms now under consideration.* 



[* The following note is inserted in place of another, which, by an 

 error of the printer, is in the Quarterly Journal of the Geological 

 Society incorporated with the text : 



Mr. Billings has ascertained, since this paper was written, that one of 

 the species included in the genus drchceocyathus, has silicious spicula 

 which would place it with the sponges. But two other species of the 

 genus have, in accordance with his original description, a chambered 

 calcareous skeleton, which is, in my opinion, similar to that of Foramin- 

 ifera. (Memoirs of the Geological Survey of Canada, Nov. 1861, and 

 reprint of the same in 1864.)— J. W. D.] 



