24 G. F. Harris — Geology of the Gironde. 



The upper zone contains numerous molluscs which serve to fix 

 the correlative age of the deposit. Amongst them may be cited 

 Bostellaria (Bimella) fissurella, Calyptraa trochiformis, Turritella 

 sidcifera and Diastoma costellata. These have a distinctly s Calcai re 

 Grossier appearance, but M. Fallot says ' that the bed being above 

 the Limnea lonyiscata limestone places it rather on the horizon of the 

 Upper than the Middle Eocene of the Paris basin. I cannot help 

 thinking, however, that correlation by means of fresh-water lime- 

 stones containing long-range species is a rather doubtful proceeding. 

 These local fresh- water beds are liable to occur at various horizons 

 in the Eocene and Oligocene. 



At Grave, Bonzac, and other places, clay with PalmotTierium is 

 classed with the Upper Eocene, but the higher portions of the beds 

 are believed to be the equivalents of the horizon to be next described. 



Certain marls and loose sandstones above the Sismondia limestone 

 which crop out in the same districts as that bed, are of doubtful age. 

 They are divided into two parts, the upper being characterized by 

 Anomia girondica, and the lower by Ostrea bersonensis. The upper 

 series at the quarry of Meynieu near Vertheuil contains a fauna 

 having considerable affinities with the Tongrien (Oligocene). They 

 seem to be passage-beds between the Eocene and Oligocene. 



Oligocene. 

 The beds classed under this division of the Tertiaries were, all of 

 them, called Lower Miocene by old authors, and much confusion 

 has thus arisen, though the alteration was in some respects a very 

 good one. I would particularly call attention to the fact that in 

 consequence of this change in nomenclature a great many of the 

 excellently-preserved fossils in our Museums labelled "Dax 2 (Gaas) 

 Miocene," ''Bordeaux Miocene," etc., are not in reality Miocene 

 fossils, but Oligocene. Where the precise locality is attached to the 

 specimens, it ought not to be difficult to assign them to their proper 

 age, and even where this information is not given, the colour of the 

 matrix of the bed, together with the correct identification of the 

 species, enables any one familiar with the beds in the field to say 

 definitely, in regard to the majority of the specimens, whether they 

 are Oligocene or Miocene. Further, the particular formation of 

 either division to which they belong could also by this means in 

 most cases be indicated. The recognition of these facts opens up 

 the question whether, in describing species supposed to be new to 

 science, English palasontologists have given that close attention to 

 the so-called Miocene species (really Oligocene) of the Aquitaine 

 basin that they might have done. We are all aware of the tendency 

 of many authors to " create " new species almost solely on the ground 

 that they occur in different, rather widely separated, subdivisions 

 from other species having the closest affinity to them, and which, if 

 they only occurred in one and the same deposit, would be regarded 

 as specifically identical or varietal at most. For instance, suppose 



1 Op. tit. p. 8. 



s Dax is in the Department of the Landes, hut seeing that many authors allude to 

 the locality in connexion with Bordeaux Miocenes, I thought it desirable to mention 

 the place. 



