PRESTWICH — BRITISH AND FOREIGN TERTIARIES. 10.7 



are met with in the overlying Sables moyens. This setting-in of 

 newer forms appears, however, from a recent discovery of jNIr. Ed- 

 wards, to be much more marked in this country at a spot near Bram- 

 shaw, between Lyndhurst and Salisbury. The superposition of the 

 bed is not shown ; but, judging from its place of outcrop and its fossils, 

 I should place it at the top of the Bracklesham series. From this bed 

 1 03 species of Mollusca have been obtained, and of this number 45 

 are Barton species — a much larger proportion (in the ratio of 43 to 30) 

 than exists at Bracklesham. As in the lower Bracklesham zone, in 

 which we have a larger preponderance than in France of the fossils 

 of the next underlying series, so in this upper one we have a nearer 

 agreement with the fauna of the overlying series ; for in France, taking 

 the total of the Calcaire grossier species, 35 per cent, range upwards, 

 whilst at Bramshaw the proportion passing upwards is 43 per cent. 

 Not only is the proportion of Barton species so much larger in this bed, 

 but there are also found in it several species which in France do not 

 appear until the period of the Sables moyens. In England, on the con- 

 trary, some of these latter species* have not been found in the Barton 

 Clays, presenting us therefore with the anomaly of species charac- 

 terizing the upper zone of one formation in England, absent in the 

 synchronous zone in France, migrating to and flourishing in that 

 latter area in the next overlying series, whilst in the contemporaneous 

 English beds they are wanting. This in fact is a phsenomenon ap- 

 parently common throughout the Eocene series, and should render 

 us very careful in drawing any conclusions from observations upon a 

 limited number of organic remains. 



Although the four subdivisions of the Calcaire grossier are 

 generally maintained and sufficiently w^ell marked, still it must not 

 be supposed that they are independent. On the contrary, it is often 

 difficult to draw a line of separation between them. Not only do 

 they pass one into another by lithological characters, but also by 

 organic remains ; yet on the whole these latter, taken in conjunction 

 with the mineral mass, are sufficient to give to each subdivision a 

 peculiar type and character of its own, not only over the whole 

 French area, but in some instances shadowing their features in ad- 

 jacent Tertiary areas of the same age. 



The cause of the great actual difference in the French and English 

 series arises probably from the more marine conditions maintained 

 in this country throughout the Calcaire grossier period — conditions 

 resulting, I believe, from a more constant and rapid subsidence of 

 the English area, keeping a moderately deep sea, and serving to 

 receive comparatively thick deposits during the whole of this period ; 

 whereas the movement extending only in part and in a very minor 

 degree, if at all in many places, over the French area, we there find 

 evidence of the sea being silted up, shut out, and replaced by fresh- 

 water lakes and lagoons. In all this inquiry it is to be noticed 

 that, although the species in the two countries differ considerably, 

 yet on the whole the same genera are common in both : not only so, 

 but the species are generally developed in somewhat the same ratio 

 * As the Ce.rithium Bouei and J'olufa mutata. 



