176 ME. C. EEID AND ME. J. GEOTES OX THE [vol. Ixxvii, 



too rare in most strata to be of much assistance. For the corre- 

 lation of far-distant deposits we need some group of fossils easily 

 dispersed, and therefore widely spread, having many generic and 

 specific forms of limited range in time, Avith specimens occurring 

 in profusion in a determinable state. In short, for zonal work in 

 freshwater strata we require a group somewhat equivalent to the 

 graptolites in wide distribution and characteristic forms. 



One group seems to possess all these qualities, if we can obtain 

 sufficient material. The Charophyta are submerged aquatic 

 plants, of which the living genera and species have generally wide 

 ranges, and the peculiar fruits with their spirally-coiled cells offer 

 many characters for specific determination. They usually occur 

 in profusion in the places where they grow, and they grow nearly 

 everywhere in pools, lakes, and brackish- water lagoons. The fruits, 

 being commonly calcified, are found in most deposits that contain 

 freshwater mollusca : in fact, many of the so-called ' shell-marls ' 

 would be more properly described as ' Chara marls.' 



Though for many years the fossil Charophyta have been gathered 

 from various freshwater deposits, it was not until one of us settled 

 in Hampshire, and began to collect more fully the plants of the 

 Hordle Cliffs, that the idea of using Charophyta as zone-fossils 

 took shape. A slight search showed that in these Tertiarj" strata 

 there were many unknown forms, some apparently of peculiar 

 generic types. Concurrently with this work on the Tertiarj" species, 

 we undertook the examination of the Purbeck Charoph^'ta, with 

 the result that the various Purbeck forms seem all to belong to 

 stranee extinct o-enera. The Swiss Miocene and the Austrian 

 Lower Eocene forms, only as yet slightly examined, seem also to 

 belong to well-marked groups of limited vertical range. 



These indications of the value of the group for the purposes of 

 zonal work, combined Avith the discover}^ in a short time of so many 

 undescribed types, has induced us to undertake the working-out of 

 the Cbarophyte flora of the zone most thoroughly searched — the 

 Lower Headon Beds, We should like to have investigated the 

 whole of the Hampshire-Basin Eocene and Oligocene deposits, also 

 to have estahlished the correlation of the fi'eshwater strata with 

 those of the Paris Basin ; but the War made it impracticable to 

 get about in certain areas, and also made it impossible to consult 

 the foreign museums, especially those of Paris. 



"In the Hordle Cliffs of the mainland of Hampshire, the strata 

 l)elow the superficial gravel belong certainly to the Lower Headon 

 Series : a small outlier of the marine Middle Headon, formerly 

 seen, having now been entirely destroyed by the encroachments of 

 the sea. There is no possibilitv, therefore, that any of our speci- 

 mens can have come from any but this one horizon. The Headon 

 Beds, though placed by British geologists, following Judd, in the 

 Oligocene, and lithologically more closely allied to the Oligocene 

 above than to the Barton Beds below, are in reality on the same 

 horizon as the Calcaire G-rossier of the Paris Basin, and this for 



