On the Elsworth Rock and associated Strata. 103 



two northern bands represent the Elsworth beds, it will be seen 

 that the apparently thick stratum of Bluntisham becomes very 

 thin at Elsworth, being represented by the layers mentioned in 

 the bed of the brook, and that they have ceased to exist at 

 Bourn. The only fact bearing against this view is, that, so far 

 as known, the fossils from the clay above the rock at Elsworth 

 are not identical with those from the clay near Needingworth, 

 but very different. If the other view is taken, the St. Ives rock 

 will be an inferior band separated by a considerable thickness of 

 clay from that above. Now, if the upheaving force met with 

 anything like the same amount of resistance to the north which 

 it did to the south, it will be clear that as Bluntisham is 3 miles 

 north, and Elsworth about five miles south, of St. Ives, there 

 ought to be an anticlinal outcrop of the St. Ives rock in the 

 neighbourhood of Fenstanton, that is, two miles south of its 

 St. Ives outcrop, where it should dip south into the clay, so as 

 to pass under the rock of Elsworth. However, as Bluntisham 

 is on high ground, it will be necessary to allow a further exten- 

 sion of a mile or two north, to balance its height. And so it is 

 highly probable that the pressure from below was greatest very 

 little to the south of St. Ives. Now, in the village of Coning- 

 ton, a mile and a half north of Elsworth, and three miles and a 

 half south of the pit showing the rock at St. Ives, a well was 

 sunk to a depth of 250 feet; and herein, after digging for 100 

 feet, a rock was pierced 5 feet in thickness. It has already been 

 shown that the rock will dip south. If we suppose this incline 

 to be the same as between Elsworth and Bourn, when the rock 

 reached St. Ives, it would only be 18 feet below the surface ; 

 and as no rock is found there at that depth, and as the angle of 

 the incline may be expected to increase as the plane inclined 

 approaches nearer the central action of the inclining force, and 

 also as some allowance must be made for possible difference of 

 heights at the places mentioned, the evidence will be perfectly 

 conclusive that this deep-seated rock of Conington is really the 

 " old red rock " of St. Ives brick-yards, and, therefore, that the 

 Elsworth rock, 130 feet above it, is essentially identical with the 

 limestone at Bluntisham. And this explains the discrepancies 

 between the fossils from the clay above the rock at St. Ives and 

 those met with in the clay at Bluntisham, while the character- 

 istic fossils of the Elsworth clay are, so far as is yet known, iden- 

 tical with those of the latter place. At present I have no fur- 

 ther evidence of the extension, in a longitudinal direction, of the 

 Elsworth rock, which has thus been traced for a distance of 

 eleven miles, with every circumstance to indicate that it extends 

 far both to the north and to the south of these limits. 



It will, however, be readily seen that this argument is not 



