516 



More remains to be noticed in this example. In our former Paper 

 we contended that the "nummuline layer" is not a calcareous " proper 

 wall" independent of the " chamber casts/' but merely their external 

 serpentine changed into its asbestiform condition of chrysotile ; and we 

 gave an illustration, "selected out of a number of the same kind," 

 which "demonstrated" the truth of our view :* this case has been totally 

 ignored. It is singular that Dr. Carpenter's section is quite prolific of 

 precisely similar cases. The one under notice, which is equally de- 

 monstrative, shows the edge of the serpentine, at a, distinctly cut with 

 lines, frequently corresponding in their distances from one another 

 with the diameter of the adjoining separated aciculi, into the bounding 

 surfaces of which, in point of fact, they run. The same phenomenon is 

 displayed at the upper portion of the opening, where the divisional 

 lines are only just appearing. With such modifications as those lettered 

 a, b, c, and d (and many more that we are prepared to bring forward), the 

 assertion is inexplicable to us that the "cell wall in no instance presents 

 the appearance of chrysotile, or of any other fibrous mineral, when exa- 

 mined with care under sufficiently high powers"-]- (Dawson). 



In order to explain, on the " eozoonal" view, the various appearances 

 presented by the " nummuline layer," it might be suggested, as in 

 another case, that the compactness of the aciculi is the result of 

 " metamorphic changes" to which these parts have been subjected; 

 thereby causing them to lose their typical character. Thus, in the case 

 under Figures 1, and 2, d (PI. XLL), it is conceivable that, as the siliceous 

 aciculi ("casts of pseudopodial tubules") are contained in a calcareous 

 matrix, the substance of the latter may have been removed by per- 

 colating waters containing carbonic acid; thus allowing the aciculi 

 free to enlarge, through intumescence, and become juxtaposed. ;£ But 

 this explanation totally fails to account for the asbestiform condition 

 of the " cell wall :" for, by no possible means, or by no sound process of 

 reasoning, can it be supposed that the separated aciculi could be con- 

 verted into the imperfectly developed divisional structure of the modi- 

 fication, lettered a, which is indisputably incipient chrysotile. From 

 the one extreme, of separated aciculi, to the other, of imperfectly 

 chrysotilized serpentine, there is an unbroken passage — an insensible 

 gradation — demonstrating the " nummuline layer" to be of purely 

 mineral origin. This conclusion is equally proved by the perfectly 

 corresponding changes that occur in veins of chrysotile, as shown in our 

 former Paper, and to be further elucidated in the present one.§ 



* "Quarterly Journal of Geological Society," vol. xxii., PI. XIV., fig. 2. 



f " Quarterly Journal of Geological Society," vol. xxiii., p. 262. 



X Vermiculite, related to logaote and serpentine, swells out on the application of 

 heat ; so do other hydrated minerals, as the zeolites ; also the fibres of chrysotile on ex- 

 posure to air (Delesse). 



§ The hypothetical explanation of the presence of carbonate of lime between the 

 aciculi, advanced in our previous Paper, will be supplemented by additional evidences 

 given in the section on the " Mineralogical Considerations." 



