80 UB.. C. B. WEDD ON THE CORALLIAN ROCKS [Feb. I9OI, 



III. Outcrops north op the Ouse. 



We may turn now to the St. Ives district, north of the Ouse. 

 From the well-known exposure of the limestone, in the brickpit 

 west of that town, I traced the yellow oolitic limestone westward 

 along the escarpment as far as Houghton Hall. A fossiliferous 

 rock had been noted here by Mr. Cameron. Appearances indicate 

 that the outcrop probably strikes northward from here under Drift. 



About 400 yards south-south-east of Houghton Hall, in material 

 dug from the weathered rock, I found a block of hard bluish lime- 

 stone full of Serpula and Exogyra, like that of lied Hill Farm and 

 elsewhere. 



At the eastern end of the section in the brickj-ard, the easterly 

 slope appears to exceed the dip of the beds, and the outcrop is 

 evidently cut back northward. About | mile farther north, 500 

 yards east- south -east of the first milestone from St. Ives on 

 the road to Ramsey, on low flat ground, I found sections of the 

 Rock in ditches. It consists of yellow marl and ironshot oolitic 

 limestone, very fossiliferous, and contains : — 



Ammonites (Perisphinctes) plicatilis, 



Sow, (abundant). 

 Gryph(Ba dilatata, Sow. (abundant). 

 Fecten articulatus (?) Schloth. 



Pecten Jihj'osus, Sow. 



Collyrites hicordata, Leske (abundant). 



Pygaster umhreUa, Ag. 



Vermilia sulcata (?) Sow. 



The brickyard north of St. Ives, mentioned by Seeley and Roberts, 

 where similar rock was said to dip eastward under clay, is nearly 

 i mile south-south-east from here, on higher ground. I found 

 fragments of the same rock in the floor of this pit. Evidently the 

 outcrop between the two brickpits forms a loop to the northward, 

 as suggested by the surface -con figuration (see map, p. 74). 



Farther east is the third brickyard of Seeley and Roberts, north- 

 east of St. Ives, where a similar rock was believed to occur in 

 the floor of the pit. The brick-pit is excavated in the south-western 

 flank of a tract of rising ground, with low ground on the north-west, 

 west, and south. In the eastern side of the pit, and outside in the 

 neighbouring field, are exposures of yellow marl and ferruginous 

 somewhat oolitic limestone, with Ammonites plicatilis and Gryphcca 

 encrusted with Serpula. The sections are obscure, but the Rock 

 seems to be several feet thick, and must dip north-eastward here 

 at a rather higher angle than usual, for immediately to the north 

 black laminated clay is seen, markedly different from the blue clay 

 worked in the west of the pit. This difference is recognized by 

 the workmen, who state that the dark clay in the north-eastern 

 corner is of no use for brick-making. The black clay is, I think, 

 certainly Ampthill Clay. Yellow rock-debris are seen in the floor 

 of the middle part of the pit, and must crop out again in the 

 north side, for in the western part stiff blue Oxford Clay is worked, 

 dipping slightly north of east at about 4°, as shown by a thin white 

 stone-band ; this is evidently lower than the yellow limestone. I 



