168 PEOF. J. W. JUDD ON THE OLIGOCENE 



First in importance we have the strata containing the three marine 

 faunas, which, as we have seen, are so well characterized and are so di- 

 stinct from one another. The name of Bartonian is now accepted 

 everywhere for the strata containing the first and lowest marine fauna 

 and their continental equivalents. For the beds which contain the second 

 marine fauna, I have proposed the name of the BrocJcenhurst series, 



For the beds containing the third and highest marine fauna, I 

 propose to retain the name of the Hempstead series. It is a very- 

 unfortunate circumstance that, in selecting this name, Prof. Edward 

 Forbes was labouring under a mistake. As I have already pointed 

 out, Hamstead, in the Isle of Wight, is spelt in a different manner 

 from that of the well-known London suburb ; while the name of 

 Hempstead is not only quite unknown in the Isle of Wight, but 

 belongs to localities in Essex and Hertfordshire. IsTevertheless the 

 inconvenience of changing a name which has been so generally 

 adopted both in this country and abroad is so manifest that I do not 

 propose to interfere with it. It is desirable, however, to restrict its 

 application to the more purely marine strata constituting the upper 

 100 feet of the section in the Isle of Wight. The grounds on which 

 Prof. Forbes separated the estuarine marls below the marine strata of 

 Hamstead from the Bembridge marls below can now be shown to be 

 very unsubstantial. The occurrence of a lignite seam like the 

 " Black band " of the Hempstead series is too common a circum- 

 stance in the case of these fluvio-marine beds to warrant us in 

 making it the limit between two series of strata ; while the first 

 appearance of Hydrohia (or Bissoa) Chastelii, to which Prof. Forbes 

 attaches so much importance, loses its significance now that, as is 

 shown by Prof. Sandberger, the shell in question is recognized as a 

 freshwater form belonging to the genus Euchilus. 



In dealing with the estuarine strata which separate these three 

 marine groups, the Barton, the Brockenhurst and the Hempstead, 

 I am impressed with the desirability of avoiding the multiplication 

 of names for small and local groups of these strata, where no good 

 palseontological grounds can be shown for such divisions. The strata 

 are so inconstant in their mineral characters, and it is so manifestly 

 impossible to trace them at the surface by the methods at the com- 

 mand of the geological surveyor, that such minute subdivision of the 

 beds can tend only to the confusion rather than to the elucidation of 

 their relations. 



I therefore propose to extend the name of the Headon series so as 

 to cover all the beds between the Barton and the Brockenhurst series, 

 and to call all those strata which, as we have seen, belong to the 

 palaeontological Zone of Oerithium concavum, the Headon ^roup. 

 The divisions of Upper, Middle, and Lower Headon cannot, as I shall 

 show, be traced to any distance ; and we therefore regard the aban- 

 donment of these smaller subdivisions as an actual advantage. The 

 Headon group, as now constituted, will embrace the whole of the true 

 Headon series, with certain others both above and below it. 



To all the beds between the Brockenhurst and Hempstead series 

 I propose to apply the name of the " Bembridge group," which also 



