382 Correspondence — Prof. J. W. Judd. 



species of oyster), by being audibly full of water when sbaken. 

 Many contain only sand, lime or earthy matter, perhaps the residue 

 of fossils destroyed. 



Collecting the water-bearing nodules is somewhat akin to choosing 

 cocoa-nuts at the greengrocer's. We pick up one after the other from 

 the ground, rejecting the light ones, and those that give forth no 

 sound, in favour of those which, like the cocoa-nuts with milk, bear 

 unmistakeable evidence of containing liquid. 



What the nature of this liquid may be, 1 or what duration of time 

 has elapsed since it was sealed up in these portable reservoirs, is not 

 for me at present to say, having as yet made no minute examination. 

 The specimens contained water when we picked them up, as did 

 others when split with the hammer. Since bringing them home, 

 they have been in a warm room, and the water from some reason, 

 probably increased temperature, has evaporated or disappeared. The 

 iron pan which forms the walls of the cavity may be porous, 

 and 1 have placed them in a vessel of water, expecting them to 

 become water-bearing nodules again; the phenomenon would then be 

 probably explained, by supposing that during periods of wet these 

 nodules absorb the water percolating through the Greensand. 



It then becomes a question whether these nodules may not be 

 a cause of diminution in the water supply ? in districts where they 

 are largely developed. But against the absorption theory, remains 

 the fact that the weather was very warm and fine when the nodules 

 were gathered, and the recent heavy rains had not set in. 2 



A. G. Cameron, 

 Bedford. H. M. Geological Survey. 



ON THE TERM NEOCOMIAN. 



Sir, — In writing his article upon the above subject, in the last 

 Number of the Geological Magazine, my friend Mr. Jukes-Browne 

 appears to have been labouring under a curious and very unfortunate 

 misconception. He says : — 



" For many years English geologists were content with the nomen- 

 clature employed by the earlier students of the Cretaceous system — 

 Webster, Murchison, Mantell and Fitton. In 1864, however, the 

 French term Neocomian was introduced by Prof. Judd, who adopted 

 it for the Cretaceous portion of the Speeton Clay, and Sir Charles 

 Lyell subsequently used it as a synonym for the whole Lower 

 Cretaceous series in England, as distinct from the Upper Cretaceous 

 series or the beds lying above the Lower Greensand." 



Through the whole of the following pages, the writer of the article 

 enlarges upon this text, treating myself as responsible for the error, 



1 Since writing the above, it has been suggested to me that an analysis of the 

 ■water might be made. This would of course be a valuable guide to the source of 

 supply. — A. G. C. 



* For a description of the mode of formation of the ironstone concretions, see 

 Penning, Geol. Mag. Dec. II. Vol. III. p. 218. Geology of Cambridge, Geolo- 

 gical Survey Memoir, p. 12, Penning and Jukes-Browne. 



