On the Elsworth Rock and associated Strata. 101 



is on higher ground, but the rock at Elsworth dips to the east ; 

 hence this stratum will probably be a band some depth under- 

 neath it. 



Northwards from Elsworth to St. Ives, the country is perfectly 

 flat, and occupied at the surface almost continuously by gravel, 

 the rock having disappeared, probably by denudation. But, on 

 approaching St. Ives from the south, a ridge of high land is 

 seen flanking the town on the west ; and on carefully exploring 

 a brick-yard at the base of it, I found abundant remains of a 

 rock which an old brickmaker told me once extended con- 

 tinuously all over the pit to a thickness of 3 feet, quite at the 

 surface, and sometimes parted into two beds by an intervening 

 layer of clay. 



Where visible, the rock here is much weathered, but is the 

 same kind of reddish-brown deposit, full of oolitic grains, which 

 occurs at Elsworth. It has long been mistaken for drift, and, as 

 such, is alluded to in the ' Oolitic Echinodermata f but, though 

 quite at the surface, thin, and often overlain by boulder-clay, 

 there cannot be the least doubt that it is a solid rock of Secondary 

 age accumulated on the clay below. Passing a little to the east, 

 I learned that, in another brick-pit there, a rock had formerly 

 existed, but was now all removed at the surface, having dipped 

 down into the clay to the east of the pit. And still further to 

 the east, at the point where the roads branch to Needingworth 

 and Somersham, it appeared that, in another brick-yard, they 

 sometimes, when digging, came down upon a floor of hard stone, 

 which they have never attempted to get through. To one going 

 over the ground, the conclusion is irresistible that the rocks men- 

 tioned at all these pits are one deposit dipping down to the east; 

 but whether this rock is an extension of that of Elsworth, or 

 another bed inferior or superior to it, is a vei*y complex question, 

 difficult to answer. 



llather more than two miles N.N. E. of the last-mentioned pit, 

 and three miles from the pit exposing the rock at St. Ives, is the 

 Bluntisham cutting of the Eastern Counties Railway. This is a 

 piece of high land, which has been cut through to a depth of 

 about 40 feet, and yet the base of the cutting is so elevated that 

 the line descends towards St. Ives at an incline of one foot in 

 less than two hundred ; so that the rails here cannot be less than 

 50 feet higher than they are two miles to the south. Now, in 

 this cutting, just below the surface, is found a rock, of a grey- 

 blue colour and unknown thickness, which was so hard that it 

 had to be blasted in laying the railway drain. I have a frag- 

 ment, containing iron-shot oolitic grains and shells, quite resem- 

 bling the rock of Elsworth. It extended continuously for dis- 

 tances of about 100 feet, when, as I was informed, short inter- 



