CRETACEOUS SERIES IN LINCOLNSHIRE AND YORKSHIRE. 361 



Proceeding round this curve to the east-north-east, we find a rapid 

 change in the thickness and character of the lied Chalk ; but how this 

 change comes on, or whether the thickening of the bed is regular or 

 irregular, there exists no evidence to show, owing to the broken-up 

 condition of the base of the Chalk. 



That it thickens rapidly is certain ; for on Seraggiethorpe Brow, 

 about 5 miles north-east of Wharram Grange exposure, the Eed Chalk, 

 though much broken up, was seen by Mr. Strangways to be 10 feet 

 thick. About 5 miles more to the east it is proved to be 25 feet 

 thick in the well-boring at East Heslerton, and the deposit is roughly 

 described as a '^ clay," and therefore more like the Speeton material 

 than that along the western escarpment. A little more than 3 miles 

 further, at Potters Brompton, Prof. Blake considered that 10 feet was 

 shown; but its full thickness is certainly not seen here. The 

 remaining inland exposures are minor ones and tell only of the 

 extension of the Ped Chalk to Speeton, where there is at least 30 

 feet of it. 



My own opinion, based on a general knowledge of the " behaviour " 

 of the chalk, is, that in all probability the thickening is fairly 

 regular and increases gradually to the east. 



Chemical analysis and examination by the microscope show at 

 once that we have reached here another area of deposition, and that 

 the augmentation in the thickness of the Eed Chalk is due to fine 

 mud deposited contemporaneously with the calcareous matter. 



The incoming of so much inorganic material testifies to the 

 existence of a current bringing detritus from continental land and 

 therefore an approach to another limit of the Cretaceous sea. 



The gradual lateral passage of the Gault mud of Bedfordshire and 

 Cambridgeshire into the calcareous deposit which is its equivalent in 

 north-west Norfolk shows that there was a deep sea to the south of 

 Lincolnshire, and that the mud is not likely to have come from 

 that direction in early upper Cretaceous time. 



It would appear therefore more probable, considering the nature 

 of the deposit along the western escarpment of the Wolds, that land 

 lay to the iST. and N.E., and that the current carrying detritus came 

 from this direction. 



We have in Yorkshire a close analogy to that which occurs in the 

 Gault of West Norfolk ; there a gradual lateral passage can be 

 followed from the inorganic sediment of the Gault to a clear and 

 probably deep-water deposit, in which Poraminifera and calcareous 

 particles form the chief part of the material ; here the reverse is the 

 case, and the passage is from a deep- to a shallow-water deposit, 

 within the range of mud-bearing currents. 



Chalk Marl. — The base of the Chalk Marl through Lincolnshire 

 continues to be marked by the bed of compact limestone, the repre- 

 sentative of the " Sponge-bed " of Hunstanton ; and although this 

 can be followed along the western escarpment of the Yorkshire 

 Wolds at their most north-westerly point it can scarcely be separated 

 from the Red Chalk. 



Above this 4 or 5 feet of grey gritty chalk retain the character 



