4 Transactions of the Society. 



thus the augular character of the detrital grains of those minerals 

 would be explained. 



What may be regarded as additional evidence proving the 

 shallow-water origin of these Cretaceous limestones and sandstones, 

 is shown by the occurrence of some drift-wood found in the same 

 beds and partly coated with Inoceramus-be&rmg mud and sand. 

 A specimen of this wood, given to the Museum collection by 

 Mr. Williams, was seen to be much corroded and bored by some 

 organism. A microscopical examination of a thin section of the 

 wood showed the presence of pitted cells, but as these are typical 

 of both Conifers and Cycads, it is impossible to say to which group 

 of plants it belongs. The Conifers, however, being more abundant 

 in Lower Cretaceous times, the probability weighs in favour of 

 the latter type of vegetation. Instances are not unknown where 

 fossil drift-wood has occurred in sediments of moderately deep- 

 water origin, as in the occurrence of coniferous wood in the English 

 Chalk at Croydon found by Murton Holmes.* Under ordinary 

 circumstances it is, however, more usual to find fossil drift-wood 

 associated with littoral deposits, as for example, in the shallow 

 deposits of the Gault at Folkestone, and in the Lower Greensand 

 of the Isle of Wight. It is easily conceived that a piece of floating 

 wood soon becomes the object of attack from various marine para- 

 sites and boring animals, which render it just heavy enough to 

 sink and to become inclosed in the mud of the sea-bed. On account 

 of its comparatively low specific gravity it stands a good chance of 

 being again cast ashore and commingled with the sand and shells 

 of the sea-shore. 



* See Fossil Plants, by A. C. Seward, 1898, pp. 61-2, fig. 8. 



