Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/410

 coloured fluids of considerable density or tenacity: should the layers of the several fluids have been straight, the curved and wavy appearance is given by producing short and partial disturbances in different parts of the compound. There can be very little question that this rock must have been coloured by a similar operation while in a semifluid state, for on no other hypothesis can the peculiar distribution of the two coloured substances through the whole mass be explained. The continuity of the lines of colour precludes all possibility of a succession of deposited layers, otherwise than in those very lines, and affords at the same time a proof, if any were wanting, that the fissile property of this killas has not been the result of stratification. The whole must in fact be considered as formed either of one deposit, of a semifluid red mud, coloured afterwards by a mixture of blue mud, or of successive layers of red and blue mud. In this state the application of external disturbing force has produced the peculiar contortion here exhibited. It is evident that the theory of softening used to explain the contortion of rocks, is in this case insufficient: a species of fluidity is requisite, otherwise the elongation and narrowing of the blue lines, could not have taken place.

Having established the necessity of consolidation from a fluid state, it remains to ascertain by what powers both the fluidity and the consolidation were effected. There is no difficulty in supposing that the requisite state could exist in a mere mixture of clay and water at the ordinary temperature: but when we consider the large proportion of water requisite to maintain that state in a given quantity of clay, it is difficult to conceive how the disposition of its parts could have been preserved during the great contraction which it must have undergone in the act of consolidation.