CHAP. 7.] ROCK FORMATIONS. .SUB-NUMMULITIC. 67 



Short of absolute intercalation this group presents many appear- 

 ances of conformity to the traps, though its lowest 



Conformity to traps. i o 



beds are often so soft and semi-soluble that they 

 hardly retain their forms sufficiently to show clean sections. These 

 lowest beds are generally -the white or variegated unctuous breccia, having 

 sometimes a large concretionary structure, with which that of the under- 

 lying uppermost trap flow coalesces in a peculiar way, the spheroids of 

 the brecciated soft bed having centres of the same nature as the trap 

 below, surrounded by coatings each more nearly approaching the character 

 of the containing rock, which has altogether a strongly volcanic appear- 

 ance. No case of unconformity to the traps is known ; mere regularity 

 of succession would not of course establish the contrary, but the general 

 arrangement of the band — surrounding, following, and overlying the 

 highest of the traps, — indicates such conformity as might exist between 

 the later (probably more intermittent) trap flows, and still newer volcanic 

 eruptions associated with the deposits of a succeeding period. 



The most volcanic-looking beds have often, in hand specimens, a 



' derivate' appearance, resembling chemically 

 Petrological appearance. 



metamorphosed states of some ' ingenite,'* such as 



poi-phyritic dolerite, magnesian amphibole, or pyroxene ; but the manner 

 of their occurrence is that of normal amorphous ash, perhaps sub-aque- 

 ous lava, or possibly volcanic mud — that is to say, if chemical metamor- 

 phosis has taken place the whole body of the rocks has been equally 

 altered, and there is nothing in their aspect to lead to the belief that ex- 

 cavation would disclose any more original rock within theii- mass. Some 

 difference of conditions attending their production may be argued from 

 the dissimilarity between them and the bulk of the stratified traps. 

 That these conditions, however, were connected with their origin or state 



* Tonus ijroposed by my friend and former colleague Mr. Khiahan, Geol. Sur., 

 Ireland. 



( f'7 ) 



