Dr Hibbert on the Limestone of Kirkton. 279 



which Great Britain can boast, has been formed, indicative of thermal waters belong- 

 ing to the carboniferous epoch. 



A decidedly fresh-water formation is there exposed, which is characterized by the 

 absence of all marine shells, corallines, &c, and the presence of the well-known vege- 

 table remains of the coal-formation. 



But the remarkable circumstance in this limestone is its mineralogical character, 

 indicative of the very powerful chemical action under which it was elaborated. 



This chemical action appears to have been so energetic, as to have caused such 

 miscellaneous earthy matters as are found to enter into the composition of an impure 

 limestone, like that of Kirkton, to separate into laminae, and to assume a sort of 

 striped disposition, (rubane, as it is also named), resembling what I have occasion- 

 ally noticed in Auvergne, where tertiary strata have come into contact with volcanic 

 rocks. The strata, for instance, of Kirkton quarry are composed of distinct and al- 

 ternating thin laminae, some of them being of remarkable tenuity, variously consist- 

 ing either of pure calcareous matter, of translucent silex, resembling common flint, 

 or of a mixed argillaceous substance, which approaches to the character of porcella- 

 nite, or of ferruginous, or even of bituminous layers, originating probably from ve- 

 getable matter. 



Upon one of these very thin aluminous folia, which I have compared to porcel- 

 lanite, I observed the impression of a Fern, apparently of a Pecopteris, which was 

 delineated upon it like a painting upon porcelain. 



It is also remarkable, that the mixed ferruginous and carbonaceous layers which 

 enter into the structure of the limestone, often assume a sort of blistered appearance 

 upon their surface, as if from the effect of heat. 



Another effect of ancient thermal waters, may be inferred from the very singular 

 warping which the strata have undergone. The wavings which they exhibit are ex- 

 tremely remarkable upon a large scale, and it is no less surprising that the same 

 contortions should be evinced, even to a far greater degree, in small hand specimens 

 of the limestone. That this effect has been aided by a lateral as well as superjacent 

 pressure of eruptive rocks of volcanic origin, is highly probable. 



Some part of the limestone, again, shews other species of character. I collected a 

 specimen, in which a structure, globularly concretional, was observable, the surface 

 having, at the same time, a mammillary appearance. This is another proof of the 

 powerful chemical action which was excited when these limestone beds were formed. 



All these appearances tend to the hypothesis, that the calcareous beds of Kirk- 

 ton were elaborated under the action of great heat ; or, in other words, that they had 

 their origin in deep fissures, intimately connected with a volcanic focus. 



But this view does not, in fact, demand any hypothesis whatever. An inter- 

 posed mass of volcanic tufa, of a green colour, which occasionally assumes the com- 

 pactness of greenstone, is developed among the higher beds of the deposit. It has an 

 elongated, wedge-shaped appearance, and it is extended in a direction nearly con- 

 formable to the general bearing of the strata. The greatest thickness which it ex- 



