part 3] CHAROPiirTA or the lowee headojst beds. 177 



some time has been recognized. As the Charophyta also, so far 

 as they can yet be compared, lead us to the same conclusion, we 

 shall not hesitate to speak of the Headon Beds as Upper Eocene. 



The strata seen in Hordle Cliffs consist throughout of fresh- 

 water and brackish-water deposits, more or less calcareous, laid 

 ■down in wide shallow lakes and lagoons, precisely the conditions 

 in which Charophyta best flourish. The flora, therefore, is 

 rich and varied ; and this one deposit has already yielded many 

 more species than the whole of the British strata were known to 

 contain. Although so many species occur, there is no reason to 

 consider that the Lower Headon strata belong to more than a 

 single zone. There are slight differences in the species contained 

 in different seams ; but nearly all of them have now been found in 

 the thin seam of limestone, which (of all the beds) has been most 

 thoroughly searched. 



An excellent account of the succession of the beds in Hordle 

 Cliffs was published by E. B. Tawney & H, Keeping in this 

 Journal,! and we cannot do better than use their numbering of 

 the beds, altliough in some cases botanical work might induce us 

 to subdivide differently these variable and impersistent strata. 

 The total thickness of the Lower Headon strata is given by them 

 as 88 j feet, and we do not think this measurement far wrong. 



It should be remembered that for Charophyta the ordinary 

 carbonaceous plant-beds are not suitable from the point of view of 

 preservation, for calcareous fossils usually tend to decay in the 

 presence of much vegetable matter. Shaly beds also are bad con- 

 servators, for any crushing of the specimens makes it impossible 

 to extract the Charophyta in a recognizable state, though we may 

 be able to note tlie deposit as largely made up of these plants. 

 Charophyta are best preserved in the soft limestone, in the shelly 

 beds, or in sandy seams which have resisted compression. 



Our search for these plants in Hordle Cliffs has been con- 

 ducted systematically, and they prove to be far more generally 

 diffused than the published accounts would suggest. As a rule, 

 however, each seam or lenticle yields only two or three species, and, 

 in order to avoid spending time unprofitably in Avashing large 

 quantities of such material, work latterly has been concentrated on 

 ^a few very prolific seams in vs^hich the Charophyte flora has proved 

 to be exceptionally varied. 



The lowest beds of the Headon deposits (Nos. 1 to 7 of Tawney 

 ■& Keeping) are carbonaceous clays, not good receptacles for 

 Charophyta. Then follows a conspicuous band of big ironstone- 

 nodules (No. 8), which will enable the geologist to fix his position. 

 Next follow 12| feet of bluish and greenish clays, with seams of 

 sand (No. 9). This is commonly known as the Mammal-Bed, for 

 most of the larger mammalian remains have been found in it, 



^ ' On the Section at Hordwell Cliffs, from the Top of the Lower Headon 

 to the Base of the Upper Bagshot Sands ' Q. J. G. S. vol. xxxix (1883) 

 pp. 566-74. 



p2 



