378 MR H. HOME ON AMPTHTLL CIAY IN [Aug. I903, 



away or in being transported, has become tilted, and this will 

 probably limit the area of the boulder ? Mr. H. B. Woodward has 

 drawn attention to the singular absence of Jurassic outliers along 

 the western margin of the great Lincolnshire < cliff ' ; and he 

 suggests that these huge cakes and boulders were, in some cases, 

 dislodged from outliers which had become frozen to the base of the 

 ice-sheet, and were then shifted to higher levels along planes pro- 

 duced in the ice by its movement over an irregular surface. He 

 also observes that it is where the degrading action of the ice has 

 been most marked, as around the Fenland border, that the large 

 transported masses of Mesozoic strata have been most frequently 

 noted. Among examples of such masses are the disturbed 

 masses and transported sheets of Chalk on the Xorfolk coast and at 

 Trowse near Norwich, the huge mass at Roslyn Hole, Ely, 1 and at 

 Catworth in Huntingdonshire. Mr. A. C. G. Cameron came upon 

 the mass of transported Chalk, with flints and Upper-Chalk fossils, 

 which occupied the entire area of the village of Catworth, in the 

 Boulder-Clay, and 25 miles distant from the Chalk-formation. He 

 also found evidence in two places of Boulder-Clay filling deep 

 troughs at the expense of the solid rock. 2 Other well-known 

 examples are the masses of Lincolnshire Limestone at Great Ponton, 

 and the mass of Marlstone 200 yards across at Beacon Hill, described 

 by Prof. Judd ; while Mr. C. Fox-Strangways has observed a mass 

 of Lincolnshire Oolite, at least 300 yards long and 100 yards broad, 

 to the north-west of Melton Mowbray. Of special interest also is 

 the boulder of Kimmeridge Clay found above the Lower Greensand 

 in a well at Fodderstone Gap, near South Ituncton, in Norfolk. 3 

 All these occur in connection with the Chalky Boulder-Clay. The 

 large transported masses of Chalk, often with villages and forests on 

 them, on the North German Plain, which for so long were taken as 

 in situ but are now generally admitted to have been transported, 

 may also be cited. 



I am greatly indebted to Mr. H. B. Woodward, F.R.S., for much 

 help and information, and to Mr. E. T. Xewton, F.R.S., for kindly 

 determining many of the fossils here recorded. 



Postscript. 



[Dr. F. L. Kitchin, M.A., F.G.S., has most kindly supplied me 

 with the following remarks on Ostrea discoidea : — 



The sb^ls for which Prof. Seeley in 1862 proposed the name Ostrea 

 discoid ca^ have typically a roughly-circular outline. The left valve is of 

 evenly-convex form, and is marked by rough concentric folds and imbricating 

 lamellae of growth. Considerable variation accompanies an unequal duration 

 of attachment in different individuals. In some cases, the attachment appears 



1 H. B. Woodward, Geol. Mag. 1897, p. 495. &c. 



2 A. C. G. Cameron, Proc. Geol. Assoc, vol. xiii (1894) p. 356. 



3 Noted bv Mr. C. Eeid in ' The Geologv of South -Western Norfolk. &c. 

 Mem. Geol. Surv. (1893) p. 63. 



4 Aun. & Mag. Nat. Hist. ser. 3, vol. x (1862) p. 104; see also 'Jurassic 

 Eocks of Britain' vol. v, Mem. Geol. Surv. (1895) p. 136 & fig. 62. 



