288 On the Structure and Position of Eozoon Oanadense. 



Such, models were shown by the specimens recently brought 

 over by Sir "William Logan to be obtainable by submitting 

 portions of Eozoon to the action of acid, so as to remove the 

 calcareous shell ; the siliceous infiltration having not merely 

 filled the chambers, so as to give us the precise forms of the 

 sarcodic segments which occupied them, but having also pene- 

 trated into the " canal system," which extends itself from 

 these into the most solid and massive portions of the shell; 

 and, as I shall presently show in addition, having actually 

 taken the place of those wonderfully minute threads of sar- 

 code which traversed the porous walls of the chambers, so as 

 to stereotype (so to speak) their exquisitely beautiful brush- 

 like arrangement, which is thus exhibited, in by far the oldest 

 known fossil, with a perfection that could not be imitated by 

 any means we possess of preparing and displaying the existing 

 animals of the same type. 



External Configuration and Internal Structure of Eozoon. — 

 Owiug to the indefinite mode of growth of this gigantic 

 Foraminifer, and the manner in which its fossilized masses are 

 connected with the matrix in which they are imbedded, it is 

 impossible to say with certainty either what was its character- 

 istic shape, or what were the limits to the size of its individual 

 growths. There is no doubt, however, that these often 

 spread over the area of a square foot, or even more, and 

 attained a thickness of several inches; thus forming blocks 

 which bear a general resemblance to those of the massive 

 Stony Corals, such as Meandrina. The aggregation of such 

 blocks, whose continuous extension at their margins would 

 bring them into contact, so that those which originally be- 

 gan from distinct centres would become grafted, as it were, 

 together, seems to have formed Foraminiferal reefs, similar in 

 their general characters to coral reefs; save that while the 

 coral reefs of subsequent epochs, like those of the present time, 

 usually had shells, echinoderms, etc., associated with them (as 

 we know from their remains), in these most ancient reefs the 

 only organic remains yet found are those of the animals which 

 built them. In some of these reefs, from the description given 

 by Sir William Logan, the older portions appear to have under- 

 gone fossilization before the newer were built-up on the base 

 which they furnished. Thus, in the Grenville limestone, 

 the lower stratum is composed of large and small masses of 

 white crystalline Pyroxene, some of them twenty yards in 

 length by four or five wide ; these appear to be confusedly 

 placed one above another, with many ragged interstices, and 

 many smooth-worn, rounded, large and small pits. In these 

 masses of pyroxene, compact as they appear, are a multitude of 



