96 Correspondence — C. W. And reus — IT. B. Woodward. 



In conclusion, the author discusses the volume of minute cavities in 

 clay rocks and their analogues of various ages, and shows that there is 

 a distinct relation between it and the probable pressure to which the 

 rocks have been exposed. Tables are given of the pressures so calcu- 

 lated for rocks of various geological ages, the volume of empty spaces 

 decreasing in older rocks from the 32 per cent, existing in recent clays. 

 In the Moffat rocks, with very little or no slaty cleavage, the pressure 

 is calculated at about 7 tons to the square inch, while the Welsh 

 slates, with very perfect cleavage, indicate a pressure of about 120 tons 

 to the square inch. 



COE.IiESFOISriDEiN'CE. 



OFETHALMOSAVRUS : A CORRECTION. 

 Sir, — In the paper on the osteology of Ophthalmosaurus published 

 in this Magazine last year (Vol. IV, p. 202) one or two errors occurred 

 -which should be corrected. The first of these is that the figure of the 

 fore-paddle (Fig. 3) is not, as stated, a ventral view of the right limb, 

 but a dorsal view of the left. Similarly, the hind-limb figured 

 (Fig. 5) is that of the right side, not the left. Fig. 5 A being the 

 ventral view and Fig. 5 B the dorsal. In consequence of these changes 

 some of the reference letters will also be incorrect. The reason for 

 these mistakes is that all the specimens examined were completely 

 freed from the matrix, so that their position in relation to the skeleton 

 as a whole could not be determined. Recently Mr. Leeds has 

 carefully observed and marked some paddles before their removal 

 from the clay, and the above con'ections result from an examination 

 of these specimens. C. "W. Andrews. 



RE SPELLING OF PLACE-NAMES. 

 Sir, — In the January Number of the Geological Magazine, p. 45, 

 Mr. Linsdall Richardson calls attention to the spelling of the specific 

 name croivcomheia. In the Geological Survey Memoir on " The 

 Geology of the Country between Wellington and Chard " the Rhaetic 

 fossil Pteromya croiocomleia Moore, was by an oversight spelt 

 Pteromya (not Pleuromya) crocombeia. This error arose from the 

 change in spelling of Beer Crowcombe, which has been altered to Beer 

 Crocombe on the new series Ordnance Map. Changes of this kind 

 ought not, in my opinion, to affect either palaeontological or strati- 

 graphical terms. Thus I would adhere to the spelling of the Pabba 

 Shales and Scalpa Beds for subdivisions of the Lias in the Inner 

 Hebrides, despite the fact that the names of the islands on the 

 Ordnance Map have been changed to Pabay and Scalpay. 



Horace B. Woodward. 

 Hampstead. 



January 20th, 1908. 



DyniSOELXj.A.]SrE!OTJS. 



Erratum. — p. 46 (January Number), end of notice of Lord Kelvin : 

 for 24th read 23rd December. 



