part 3] THE CHAROPHYTA OF THE LOWER HEADON BEDS. 175 



8. The Chaeophtta of the Lower Headon Beds of Hordle 

 [Hordwell] Cliffs (South Hampshire). By Clement 

 Ketd, F.R.S., F.L.S., F.G.S., and James Groyes, F.L.S. 

 (Read November 22nd, 1916.) 



[Plates IV- VI.] 



Pbefatort Note. 



[The first part of this paper, written by the late Clement Eeid, was com- 

 municated to the Society very shortly before his death. It may be taken 

 as the latest expression of his views upon the position of the Lower Headon 

 Beds of the Hordle Cliifs, arrived at by the study of these beds during the last 

 foitr years of his life, when he resided at Milford-on-Sea. Except for a few 

 verbal corrections, the paper is given as he left it. 



The Charophytic remains, nearly all collected by him, had been dis- 

 criminated and partly cla.ssified before his death, but the descriptions had not 

 been written. 



It will be noted that some of his statements refer to the difficulty or 

 impossibility of comparing specimens from other areas. This is due to the 

 fact that, when he wrote, the War was still in progress. The same cause led 

 to delay in publication of the paper, for it was deferred in the hope of 

 obtaining further information as to the remains occurring in the Paris Basin ; 

 but, unfortunately, this has not been found possible. — E. M. Reid & 

 J. Groves.] 



Part 1. 

 The correlation of limestone-deposits Ij^ing in isolated basins 

 has always been a matter of much difficulty and uncertainty. 

 Thus far no group of freshwater fossils has proved sufficiently 

 widespread and characteristic for the purpose of zonal work. The 

 mammals have a ver}^ limited geographical range, their assemblage 

 depends so largely on the nature of the surrounding countrj^, and 

 their remains are usually so scarce, that they do not greatly help ; 

 besides which, in strata older than the Tertiary they almost fail us. 

 Other vertebrates, such as fishes, would also vary greatly in 

 adjoining areas. 



The freshwater and brackish-water mollusca, which are so 

 abundant, and would at first sight appear so useful, cannot be 

 depended on for the comparison of distant areas. IVEany of the 

 species are very local, and their variation under slightly changed 

 conditions is so great as to give rise to much confusion. Anj^one 

 who has worked with the genera JJnio, Corhicula, Cyrena, Palu- 

 dina, Melania, JPotamides, or LimncBa in the London and Paris 

 Basins must have felt this difficulty. In the case of the non- 

 sculptured genera, such as Paludina, the difficulty is increased by 

 a tendency to vary around a certain generic type, to which the 

 species seem to revert again and again. Indeed, in certain of the 

 molluscan genera the specific differences are so slight as only to 

 be recognizable in specimens better preserved than such as are 

 commonly available. 



The higher plants are usually very local, an(L.<fe!iei^uif<^^^^iri^'^^^7' 

 Q. J. G. S. No. 307. /O""'' ^ ''""O 



k MAR 9 1322 



