Correspondence — A. J. Jukes- Browne. 93 



outlying Eocene tracts, which were in existence during late Pliocene 

 time, were broken up and spread out by the severe climatic 

 conditions of the Glacial Period. In post-Glacial time little has 

 been added, but much removed by erosion. 



2. " On Footprints from the Permian of Mansfield (Nottingham- 

 shire)." By George Hickling, B.Sc. (Communicated by Professor 

 W. Boyd Dawkins, D.Sc, F.E.S., F.G.S.) 



These fossils were discovered in 1897 by Mr. Francis Holmes in 

 the Eock Valley Quarry, Mansfield, in a local lenticular mass of 

 sandstone intercalated in the Magnesian Limestone. The impressions 

 formed two double rows, approximately parallel, and 7 and 2 feet 

 long respectively. Nearly the whole of the longer series is in the 

 Nottingham Museum, and part of the shorter series in the Manchester 

 Museum. Both sets were made by the same species of animal, the 

 stride in one case being 8 and in the other 8^ inches. The prints 

 show a well-marked heel and comparatively slender digits, and 

 there is evidence of a membrane between the toes. There is wide 

 separation between the right and left sides, this separation being 

 more marked in the fore than in the hinder footprints. The prints 

 present some resemblance to those named Ichnium acrodactylum, 

 from the Upper Permian of Thuringia. Recently the author has 

 found other prints in the same quarry. 



ooI^I^:Es:F'OITID"^I^^o:H3. 



THE ZONE OF OSTEEA LUNATA. 



Sir, — I am very glal that Mr, Brydone is publishing his further 

 observations on the Chalk blufis of Trimmingham, and it is clear 

 they will throw valuable light on the much disputed question of 

 the manner in which these masses were brought into their present 

 positions. 



I am sorry, however, that he should object to my choice of 

 Ostrea lunata as the index-fossil for the zone which his previous 

 observations enabled me to establish on a firm basis ; the more so 

 as his reason for objecting to the choice seems to me to have little 

 force. He admits that 0. lunata " has two characteristics of an ideal 

 name-fossil in that it is, as far as we know, almost confined to 

 the Trimmingham Chalk, and that in that chalk it always occurs 

 abundantly if at all." He thinks, however, that "it fails to fulfil 

 the most important requirement for a good zone-fossil in that it is 

 not distributed all through its so-called zone." 



Moreover, Mr. Brydone seems so sure that 0. lunata will not do 

 as an index that he proposes to rename the beds as the "zone of 

 TerebratiiUna gracilis and T. Gisei," in spite of the most obvious 

 objections. I am therefore compelled to defend my choice of a zone- 

 name from his attack upon it. 



In the first place I must ask Mr. Brydone why he asserts that the 



