208 The Rev. W. Conybeare on 



Of this Interesting spot it is hoped that the general section, and 

 the views in Plate 11. fig. 2. will convey an accurate conception.* 



* Desiring to keep that description of facts which must serve as the ground-work of 

 theory, and which seems, in the present state of science, the most useful employment of 

 the geologist, distinct from conclusions merely speculative, I have hitherto studiously 

 refrained from expressing the views which I have been led to form on the origin of basalt, 

 and of the other rocks usually associated under the general name of floetz trap. 



But while describing the striking appearances presented by Kenbaan cliffs, I cannot 

 forbear to declare the conviction which this spot first impressed upon my mind, and to 

 express my full assent to the arguments of those who maintain the igneous origin of such 

 formations. 



I would observe then that this formation is distinguished by characters so directly op- 

 posed to those which all rocks undoubtedly of aqueous origin possess, that no hypothesis 

 •which ascribes both to a common origin, can be otherwise than contradictory, and at 

 variance with itself. For 



1. Of all other formations, the least ancient are the least elevated ; but this, the most 

 recent of all, yet rivals the primitive mountains in height. 



2. Of all other formations, the degree of consolidation decreases together with its 

 age, their texture passing from crystalline through the several gradations of sub-crys- 

 talline, compact, coarse, and lastly earthy ; while in this formation, even where it rests 

 on chalk, the crystalline texture of the oldest rocks frequently recurs. 



3. Whin dykes, which are indisputably connected with this formation, differ from 

 all other mineral veins, in the circumstance of their traversing all rocks indifferently ; 

 while of other veins, particular classes are exclusively associated with particular rocks. 



Such being the negative evidence against the Neptunian hypothesis, I proceed to that 

 which is positive in favor of the volcanists ; as 



1. The identity of chemical composition in basalt and lava. 



2. The constant occurrence of trap rocks in volcanic districts. 



3. The confession of the Wernerians tliemselves, that the basalt of Auvergne is of 

 igneous origin. 



4. The testimony of those best acquainted with districts still exhibiting active vol- 

 canoes. Such persons, as Dolomieu and Spallanzaiii, have uniformly maintained the 

 igneous origin of basalt, while those who have contended against it have generally been 

 unacquainted with countries of this description. 



Having thus alluded to, rather than stated, some of the general arguments on which 

 this question appears to me to depend, I return to Kenbaan, where the basalt is seen ex- 

 tending from beneath as well as overlying the great mass of chalk, which has at one 

 extremity assumed such a curvature as would naturally result from lateral pressure ; and at 

 the other is rent, and shattered in the most exUaordinary manner, the basaltic matter 



