YENANGYOUNG. 5 13 



ment. The result is that those parts of the stream which were 



first arrested bulge out and a series of wrinkles, running transversely 



to the direction of the mud stream, are formed on its surface, 



which sometimes join each other, or in other instances burst, while 



some liquid mud flows out and fills up the unevenness between the 



wrinkles. I have described this above (page 47), but it will be seen 



that we have only to assume that this same process has been takino- 



place on a larger scale to find the explanation for the intersecting folds. 



Let us suppose that the ground on which the petroliferous beds 



were originally deposited formed a plane slightly inclined towards 



the open sea, an assumption which is quite compatible with the view 



of their deltaic origin, and let us further suppose that this plane 



eventually became horizontal. On this inclined plane a thick stratum 



of sand was deposited, followed by an argillaceous bed, and on this 



another sandy layer until the weight of these masses which were 



permeated by water and in a state of unstable equilibrium set them 



in motion. The whole mass would then slide down on the inclined 



plane until it was arrested by the change of the gradient. 



What would be the result of such a process ? Certainly some- 

 thing very similar to what is exhibited by the mud stream. The strata 

 would bulge out, they would form a series of folds, transverse in di- 

 rection to that of the movement of the strata, and they would be 

 intersected by numerous cracks and veins filled with mud, which 

 would also spread on the surface, perhaps filling out the interstices 

 between two folds. The single beds thus set in motion and arrest- 

 ed again, would certainly exhibit a great inequality of thickness 

 as well as their surface Would be very uneven, unless they are 

 filled out by " eruptive" mud. 



Now let us analyse how this theory agrees with the observed 

 facts. 



I have above pointed out (page 124) that the strange arrangement 

 of the drilled weJls suggested a peculiar structure. I have proved to 

 some extent at least, that this peculiar arrangement is unquestion- 

 ably due to the presence of some transverse folds in the upper Proma 

 1 ( '59 ) 



