520 



ments respecting the phenomenon are completely confirmed by our own 

 observations. We find a number of grains (spots) consisting of hornblende, 

 others of sahlite, a few of quartz, and some apparently of serpentine ; 

 while an occasional one appears, half composed of hornblende, and the 

 other half of sahlite. 



Dr. Carpenter has stated that we " do not attempt to offer any 

 feasible explanation of the fact," that the " siliceous mineral" forming 

 the "chamber casts" may be serpentine in one place, pyroxene in another, 

 or loganite in another." Chondrodite and pyrallolite may also be 

 added. Nevertheless, it so happens that we did make the " attempt :" 

 but we fail to find that a single argument, or evidence, has been urged 

 against our " explanation" of its being a pseudomorphic phenomenon. 

 But, whether the attempt has been successful, or not, we hold the " fact" 

 to be demonstrative of the mineral origin of the " chamber casts;" 

 since it is strictly paralleled in the case of the different mineral silicates 

 composing the grains imbedded in the Tyree pink marble, and other al- 

 lied rocks. 



Considering that the "chamber casts of Eozoon Canadense" have 

 never been found to consist of any other mineral than a silicate, and 

 that there is no reason to a palaeontologist why they ought not to 

 occur composed of a carbonate, it is singular that the latter point has 

 been so little noticed by writers opposed to our views. The use we have 

 made of the general fact, to their disadvantage, has been totally ignored, 

 though an indirect attempt has been made to invalidate it. Dr. Dawson 

 has incidentally stated that the " chambers are filled in different speci- 

 mens with" (besides the silicates alluded to) " calcareous spar, or even 

 arenaceous limestone."* In mentioning the last substance, evidently 

 the Tudor specimen was thought of; but we decidedly refuse to accept 

 the case as one to the point : and as regards the " calcareous spar," we 

 are unacquainted with any published instances of this mineral being an 

 infilling of the kind. 



Further remarks on the composition of the "chamber casts" will 

 be made in another place. 



d. " Canal System.''' — We have already stated, as our opinion, that 

 the examples which have been brought forward of this part are nothing 

 more than imbedded crystallizations, resembling arborescent silver, the 

 various kinds of dendrites in agates, branching aragonite, &c. Most 

 of the cases alluded to were brought forward by way of illustrating 

 the "canal system;" and we have nothing to complain of as to any 

 want of attention to them on the part of Drs. Dawson and Carpenter ; 

 but it is our duty to mention that the strictly homologous case of me- 

 taxits has been very slightly noticed by the one, and ignored by the 

 other. Dr. Dawson, who admits to having " not seen specimens" of 

 this mineral, puts the case aside by simply stating, that " it is evident 



;< Quarterly Journal of Geological Society," vol. xxiii., p. 263. 



