82 SIE. C. B. WEDB ON THE COKALLIAN EOCKS [Feb. I9OI, 



with many pieces of jellow oolitic limestone, containing Ammonites 

 jiilicatilis, Pholadomya, and Oryphcea encrusted with Serpula. The 

 width of outcrop here is not less than 300 yards, and may be more, 

 as the surface is obscured eastward by gravel. 



From here to Holywell the high ground makes a strong feature 

 on its western and south-western flanks, certainly composed in 

 great part of the St. Ives Rock. I saw fragments of oolitic limestone 

 in it near the eastern end of Parson's Drove, about ^ mile north- 

 west of Holywell Church. Farther south, below Manor Farm, 

 springs are thrown out at the base of the feature : close to one 

 of these, about 70 yards west of the churchyard, is a small ex- 

 posure of yellow oolitic limestone. The E-ock here forms the lower 

 j)art of the escarpment, with probably Ampthill Clay above, the 

 whole being capped with gravel. 



It has been mentioned that there is in the Woodwardian Museum 

 a collection of fossils believed to have come from Holywell, from a 

 rock like that of St. Ives. I find that the southern part of the 

 village of Holywell stands upon a gravel-capped escarpment of 

 this Rock, a continuation of the above-described feature ; some of 

 the cottages are built directly on a yellow oolitic limestone. The 

 last trace of the Rock that I have found, going eastward on the 

 north side of the Ouse, is in the field behind the Inn at Holywell 

 Ferry. 



About a mile of fenland separates this outcrop from the place 

 where I found traces of the Rock in a drain west of Swavesey. It 

 is possible that the line of outcrop between these places crosses 

 the river immediately east of here, under the fens. But the con- 

 figuration of the ground, sloping east of the Ferry at probably a 

 greater angle than the dip of the strata, makes it more likely 

 that the outcrop runs some distance first northward and then east- 

 ward down the river-valley, before returning west of Swavesey on 

 the south side. 



IV. Conclusions. 



I would here adduce the following stratigraphical evidence in 

 support 01 the generally accepted view of the identity of the 

 Elsworth and St. Ives Rocks. The limestone here traced from 

 Yelling through Elsworth to Red Hill Farm, Hilton, is un- 

 questionably one bed. It is equally certain that that traced from 

 north-east of St. Ives to Holywell is one bed ; neither is there room 

 for doubt that the latter is the same as the rock north-west of 

 St. Ives, for the intewnediate exposures accord vdth the surface- 

 configuration, the strata having a slight northerly and, in places 

 also, a small easterly inclination. !N'ow, west of St. Ives there is 

 undoubted Oxford Clay below, and apparent Ampthill Clay above 

 the limestone ; north-east of St. Ives it has been shown that the Rock 

 must separate Ampthill Clay from Oxford Clay. Farther east there 

 is certainly AmpthiU Clay above the limestone. Again in the south, 

 at Yelling, there is certainly Ampthill Clay just above, and clay of 



