Correspondence — L. Dudley Stamp. 383 



A boring through 325 feet of Gault at Iford Manor yielded 

 glauconite sand. A discussion of the analysis of this material and 

 of some previously published analyses leads to the formula RoO. 

 {4R2O3.RO).10Sid2.»H2O. 



L. J. Spencer : Ninth list of new mineral names. 



CORRESPONDENCE. 



GAULT AND LOWER GEEENSAND NEAR LEIGHTON BUZZARD. 



Sir, — I have just had the pleasure of reading Mr. G. W. Lamplugh's 

 paper on the Junction of the Gault and Lower Greensand near 

 Leighton Buzzard {Quart. Journ. Geol. Soc, vol. Ixxviii, 1922). 

 Side by side with it I have Dr. Kitchin and Mr. Pringle's paper on 

 the same area (Geol. Mag., vol. Ivii, 1920). Both papers are con- 

 vincingly written, but obviously the data relied upon by one or 

 other authority must be misleading. May I be permitted to call 

 attention to one or two points which forcibly strike an unbiassed 

 reader ? It seems obvious that one has to face in the case of the 

 Shenley Hill Limestone the problems of a " facies fauna ". Both 

 sides admit the anomalous character of the deposit whether it is 

 regarded as infra-Gault Clay or as Cenomanian. Moreover, both 

 sides make repeated references to the " continental Tourtias ", 

 especially of " Flanders ". Mr. Lamplugh likens the Ironstone- 

 breccia of the Chamberlain Barn section to a Tourtia (p. 61). 

 Personally, I cannot recall a Tourtia which answers to the description 

 given of the Breccia. Mr. Lamplugh also remarks : " Correlation with 

 the Tourtias is useless for any narrow and critical demarcation of 

 age, since the Tourtias are kiaown to occur at different horizons where 

 actually intercalated in the Cretaceous sequence ; and, where they 

 form the base of that sequence and rest directly on the much older 

 rocks, they are ' condensed ' deposits, probably covering a long 

 period, and they then generally contain many fossils not known to 

 occur in beds which lie above the Gault where it is actaally present " 

 (p. 75). Sir, in the interests of the sanity of British geology I ask, 

 are these " Tourtias " to be dismissed in this scanty fashion ? But 

 a few hours' journey from our own shores one may study a whole 

 succession of " Tourtias ", ranging in age from Albian to highest 

 Cenomanian, and even to Turonian and Senonian, the age of which 

 can be relatively and, in most cases, precisely fixed. 



In their recent paper on " The Overlap of the Upper Gault in 

 England " (Geol. Mag., vol. lix, Apiil-May, 1922), Messrs. Kitchin 

 and Pringle remark : "In any attempt to determine the zonal 

 relationships when studying deposits of clay such as the Gault, 

 subject to lateral change to other types of sedimentation, we must 

 be prepared to pin our faith entirely to the fossils. There remains, 

 of course, the recognition of the species ajDpropriate for such an 

 important use and the power to apply this evidence legitimately. 



