210 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 10, 



dolomite and ealcite are isomorphous, the mineralogical differences presented 

 by " identical forms " become at once scientifically explained. If the opinion of 

 G-ustay Rose be correct, that "serpentine is always a product of alteration " (see 

 Chem. and Phys. Geol, vol. ii. p. 417), it would not surprise us that what have been 

 called "chamber-casts" will, in some cases, be found to consist of pyrallolite, 

 chondrodite, or "green pyroxene "'(?pargasite), as, inaddition to diopside, these 

 minerals, in a finely granular state, arranged in layers and imbedded in ealcite, 

 are often mingled with the serpentine, or its varieties, of this rock in Canada 

 (see Geology of Canada, 1863, pp. 26, 465, &c.). We may here take up a point 

 alluded to in the early part of this memoir. In all the specimens of Cornish 

 Ophite which we have examined, nothing like " eozoonal " structure has occurred 

 to us, except in a variety formed principally of saponite. This mineral, in one 

 of our specimens, is here and there associated with ealcite, and in these places 

 it shows a granular structure as well developed as that characteristic of serpen- 

 tine. An object-glass magnifying 60 diameters, exhibits the granules as true 

 "chamber-casts," generally spherical in shape, but occasionally elongated or 

 cylindrical like those which have occurred to us in " eozoonal " Ophite from 

 Pennsylvania. They are aggregated in clusters, and defined by deep constrictions 

 or slight segmentations. They also occur attached to one another by stolon- 

 like necks. As yet we have failed to detect the asbestiform layer and the " defi- 

 nite shapes." Saponite, if Klaproth's analysis of it be correct, may be regarded 

 as an allomorph of pyrosclerite ; or, as it contains more water than is allowable 

 in such a view, it may be a pseudomorph of some other ophitic mineral. But, 

 whatever may be the origin of these granules of saponite, we leave the question 

 for further investigation. 



With regard to the arrangement of the granules of serpentine in 

 Ophite, the same differences which they display in this respect obtain 

 with those of pargasite and other minerals. Crystalloids of the one 

 named occur irregularly or '^acervulinely" scattered through a matrix 

 of saccharoidal ealcite ; but they are also known to occur arranged 

 with more or less parallelism in the same base. And, according to 

 Sterry Hunt, Canadian Ophite contains chondrodite in grains which 

 are sometimes so disposed as to mark "the stratification of the rock" *. 

 It is also added that apatite occurs " with the same banded arrange- 

 ment." 



Connemara Ophite is certainly in general laminated or banded in a very irre- 

 gular wavy manner, and difficult to understand, often presenting the most 

 singular and beautiful delineations. In the early stage of our investigations, 

 we considered the question as to the origin of the phenomenon to be set at rest 

 on the view that the rock had resulted from the irregular hummocky growth of 

 " eozoon." But it so happens that the same kind of lamination frequently cha- 

 racterizes the gneissoid limestones of Connemara. Sir William Logan has given 

 a representation of a precisely similar case, occurring in the Laurentian rocks 

 on the river M^dawaska (see Geology of Canada, 1863, p. 27), which consists 

 of highly contorted thin layers of gneiss, included in a thickish bed of limestone, 

 lying between masses of evenly laminated gneiss. 



From the fact that certain minerals, when imbedded in rocks, often affect a 

 definite or parallel arrangement, which is remarkably the case in graphic 

 granite, globular diorite (napoleonite), &c., it is conceivable that some of the 

 more remarkable cases of lamination presented by Grenville Ophite, instead of 

 being depositional, are the result of segregation. But whatever view may be 

 taken as to the cause of the phenomenon in general, it is quite clear, from the 

 Madawaska and the like instances, that such a cause is in no way connected 

 with organic agencies. 



Certain rocks, both eruptive and sedimentary, exhibit concretionary 

 or segregated forms simulating the granules of serpentine. Eefer- 

 * Geology of Canada, 1863, p. 465. 



