Correspondence — H. B. Woodward — A. G. Cameron. 575 



FOSSILS ON CLEAVAGE PLANES. 

 Sir, — The Eev. W. Downes, who has done good service among the 

 Limestones of Westleigh and Holcombe Eogus, in Devonshire, has 

 in a second paper on this subject [Trans. Devon Assoc. 1879] brought 

 forward the question, " Is it absolutely a universal rule that fossils 

 do never occur otherwise than on a plane of bedding ? " He notices 

 his discovery of organic remains, referred by Prof. T. E. Jones to 

 Posidonomya, on a surface of rock which is unquestionably a cleavage 

 plane. Among his specimens from Westleigh is a Spirifer manifestly 

 imbedded in a vertical position, while upon the same piece of rock a 

 Ghonetes and a Posidonomya are lying upon the plane of bedding. He 

 suggests, that the planes of separation will be determined by the 

 lines of least cohesion, and that the presence of a flattish fossil, 

 approximately parallel to the lines on which the cleavage force was 

 acting, would be apt to create a plane of weak cohesion on which 

 the external pressure would most readily take effect. We should 

 have been disposed to think that the position in which the fossil was 

 imbedded accidentally coincided with the cleavage plane, and it was 

 therefore saved from distortion. Mr. Downes however remai'ks that 

 the cleavage is of an irregular kind ; seeming often to result from the 

 folds of the hard limestone rocks crushing the intervening shaly beds. 

 The subject is one well worthy of attention. H. B. Woodward. 



RIPON SWALLOW-HOLES. 



Sir, — The Eev. J. S. Tute of Markington, near Eipon, has a notice 

 of these "natural pits" in Vol. V. Geol. Mag. page 178. That the 

 denuding agencies employed in producing them are no more dormant 

 now, than formerly, is certain. The latest subsidence occurred in '77, 

 in the West Field, near Hutton Conyers. This field is pitted over 

 with holes of more ancient date, and there also, cylindrical-shaped 

 holes, locally known as " man-holes," appear at intervals. When 

 first found, they are seen to contain water, which soon disappears. 

 To prevent animals falling in, they are filled up as quickly as pos- 

 sible. A " man-hole " that has been closed, after a time, becomes 

 again an open shaft, when the material with which it had been filled 

 is found to have been " swallowed." The subsidence of '77 is a 

 hole of very considerable dimensions, in shape an inverted cone, the 

 walls being thick-bedded red sandstone. It is fenced round. About 

 one hundred yards from it, and abutting on the footpath leading 

 from the village to Eipon, there is a shallow basin-shaped depression 

 in the surface of the soil. This place has been watched for a number 

 of years by a gentleman residing in the village, 2 who finds it sinks 

 four or five inches in a year. 



The " man-holes " are said to occur, mostly, during very wet 

 seasons, and some of the farmers think after sheep have cleared the 

 land of turnips. A. Gr. Cameron, 



Northallerton, Nov. 1879. H.M. Geol. Survey. 



1 Also a full account in a paper read at Eipon, before York. Geol. Society, in 1869. 



2 Mr. Thomas Wells, of Hutton Conyers. 



