298 Prof. Bonney—Eozoon at Cote St. Pierre. 



texture, polarization tints, or general aspect, grains occurring in the 

 cores or bands, which can be proved by cleavages and extinction 

 angles to be raonoclinic pyroxene (malacolite), from the separate 

 uncleaved grains in the calcite or the fragment-like granules in the 

 grains or masses of serpentine. Accoi'dingly, while I admit the 

 possibility of olivine being present, I think that this is not as yet 

 proved by any valid evidence. 



The observations described above indicate, I think, that the 

 Eozoon often occurs in close relation, on the one hand with a 

 fundamental mass of almost pure pyroxene or serpentine (the latter 

 being, in many cases at least, an alteration product of the former) ; 

 on the other hand, with a fairly large mass of crystalline limestone 

 containing, sometimes in bands resembling stratification, more or 

 less numerous grains of pyroxene or serpentine; the change in 

 either direction being rather abrupt. 



The concretionary habit, mentioned above, would accord either 

 with a structure purely mineral, or with an organism which grew in 

 irregular "cakes" or small reef-like masses like some Stromatoporids, 

 but in the latter interpretation there are three difficulties: (1) We 

 must assume that the organism has been infiltrated, very commonly, if 

 not always, by a pyroxene (malacolite), and this, so far as we know, 

 is not one of the silicates which usually discharges this function. 

 (2) We must account for the grains of malacolite or serpentine in 

 the external crystalline limestone. They might be regarded as 

 detached casts of " chamberlets " of the organism; but this ex- 

 planation presents some serious difficulties, which will be obvious 

 to a petrologist, while the rock undoubtedly presents a close 

 resemblance to an ordinary granular pyroxene-marble. (3) We 

 must assume that as a rule the interior of the organism perished 

 as the exterior grew, because the centre so commonly is a lump 

 of practically pure silicate. 



Whatever may be the origin of Eozoon, nothing which I saw in 

 the field suggested the probability of the specimens being " blocks 

 included in either a volcanic or plutonic mass." If the structure be 

 not a fossil organism, it is at any rate as much a part of the whole 

 rock as chert is of a limestone. There seems no reason for doubting 

 that the valley is excavated in a thick mass of crj'stalline limestone 

 included between two groups of gneiss, both of which exhibit a very 

 rudely stratified arrangement, and differ in lithological characteristics. 

 The larger masses of pyroxenite did not resemble any igneous rock 

 known to me, but as to their origin I forbear at present to speculate. 

 The felspathic vein did not resemble an igneous rock, nor did the 

 intercalated gneiss. The latter might, of course, be an intrusive 

 sill, modified by pressure ; but of this I saw no evidence, and the 

 adjacent limestone, if it has been crushed, has not retained any 

 indication of this action. To the associations of the rock-masses 

 I paid especial attention ; because, before I visited Cote St. Pierre, it 

 had occurred to me that possibly the Eozoonal limestone was a rock 

 of later date folded or faulted into an older group. But everything 

 that 1 saw led me to believe that the rocks formed a true sequence. 



