TIIK MHicKNK SERIES 573 



living .-pcrir.-, ilu- 1'iio.t-ne from forty to ninety,and the Pleistocene 

 from ninety in a fauna without specie- tliat arc more than locally 

 extinct, and finally to one that does not dill't-r from lhat of the 

 MII ruiiiidinj,' ciuintry or neighbouring sea. 



Some geoloj,'i-t>, however, prefer to take the mammalian faunas 

 as a guide instead of the molluscan, and to take note of the extinction 

 of genera rather than of the introduction of new species. Agree- 

 iin-nt on this ([motion has not yet been reached, and there are 

 differences of opinion as to the respective limits of the three series. 



I. THE MIOCENE SERIES 



A. NuMKN'CLATURE AND DIVISIONS 



Although Continental geologists have differed on the question 

 of including the stage known as Aquitanian in the Oligocene or in 

 ih<- Miocene, the latter view is now the prevalent opinion in France. 

 It is adopted not only by de Lapparent in the last edition of his 

 Traite de Geologic (1906), but its propriety has been placed almost 

 beyond doubt by Mr. G. F. Doll f us in his recent revision of the 

 typical Aquitanian fauna. 1 His examination shows that the 

 number of species of marine Mollusca common to the Stampian 

 and the Aquitanian of the Bordeaux district is only thirty-four, or 

 about 10 per cent of the total ; while the number of those 

 common to the Aquitanian and the overlying Burdigalian is 

 164 or 55 per cent, so that the affinity of the Aquitanian fauna 

 with that of the Miocene is five times as great as with the Oligocene. 

 Even when compared with the still later (Helvetian) fauna of Tour- 

 aim- a proportion of 38 per cent is found to be common to the two. 

 There is also much difference of opinion with respect to the 

 upper limit of the series, some placing both Sarmatian and Pontian 

 in the Miocene Series, but Fu.-hs and others regard the Pontian 

 Beds, which include what is known as the Pikermi fauna, as 

 belonging to the Pliocene. In the present state of our knowledge 

 it seems best to draw the line of division between these two groups, 

 and to consider the Sarmatian as the highest member of the 

 Miocene. Thus denned, the Miocene Series is divisible into five 

 stages : the Aquitanian and Burdigalian having their typical 

 development in the Bordeaux district, the Helvetian in Swit/..i- 

 land and in Touraine, the Tortonian at Tortona in Italy, the 

 Sarmatian in Austria and Southern Russia. 



The following table shows the succession of deposits which are 

 attributed to the Miocene in each of these districts. The only 

 representative of the series in the British Isles are the Bovey 

 Beds in Devonshire, which were correctly referred to the Aquitanian 



