Mr. Webster on the Strata lying over the Chalk. 167 



14. Clay with limestone and bituminous shale, containing the 

 Kimeridge coal.* 



The strata of Alum bay, now seen in a vertical position, must 

 have been originally quite horizontal, or nearly so. For it is not 

 only extremely improbable that beds of such materials should have 

 been found in any other manner, but a circumstance which I no- 

 ticed in Alum bay renders certain the original position of the sand 

 and clay strata. In one of the vertical beds, consisting of loose 

 sand, are several layers of flints, extending from the bottom to the 

 top of the cliff ; these flints have been rounded by attrition ; are from 

 one inch to eight inches in diameter, and appear to have belonged 

 to the chalk. Now it is inconceivable that these flint pebbles should 

 have been originally deposited in their present position ; and they 

 distinctly point out the original horizontality of this series. There 

 are no signs of partial disturbance in the several beds, and it appears 

 therefore that the whole has been moved together, either by ele- 

 vation or subsidence into the vertical situation. 



The strata of chalk have evidently suffered a change of position 

 at the same time with the clay and sand ; and since the vertical beds 

 of Alum bay, g, are next to the stratum o^fiinty chalk, which, accord- 

 ing to the regular order of superposition, is known to have been the 

 uppermost of the chalk series, it follows, that they are of posterior, 

 formation. Moreover, the most northern of these vertical beds is 

 a blue clay, agreeing with the London clay, a bed which always 

 lies over the chalk. 



* Other divisions of these strata have been made, and the cause of the differences has 

 already been alluded to. Not every member of the series is perfectly continuous or 

 of uniform thickness ; so that when any one is wanting, beds, usually separate, are 

 brought into immediate contact. In making a classification of these beds, those should 

 be considered as principal members, which are most rarely deficient iu an extensive tract 

 of country. 



