114 GENESIS OF THE ARIETIDJ2. 



they raise the question whether the Mediterranean forms of the Swiss Alpine 

 Jura may not have come by the way of southern France into the western Alpine 

 region. 



The very interesting and instructive essay of M. Dieulefait on the " Zone a 

 Avicula contorta et l'lnfra Lias dans le Sud-est de la France "' shows that in Prov- 

 ence a southern and northern basin may be clearly separated. The southern or 

 Mediterranean basin comprises a range of deposits reaching from the neighbor- 

 hood of Toulon and Brignolles to Draguignan, Grasse, and Nice. The basin of 

 the north and northwest, or of the Durance, encloses the valley of that river and 

 the neighborhood of Castellane and Digne in the department of Basses Alpes. 

 The ba^-in of the Mediterranean possesses a series of beds identified as belonging 

 to the zone of Avicula contorta, but there are no Ammonitinae, and all the beds 

 above these in the Lower Lias are absent. In the basin of the Durance, how- 

 ever, a very complete series of lower lias beds, including a Planorbis and Angu- 

 latus bed, has been described. M. Dieulefait has here traced the limits of the 

 Mediterranean province at a very important, and for our theory an essential 

 locality. He has shown that the sharp division between the Mediterranean 

 faunas and those of Central Europe, which, according to our conclusions, ought to 

 exist along the boundaries between the basin of Italy and of the Rhone, can be 

 actually traced in the field. 



Dumortier's extensive observations in the valley of the Rhone and Collenot's 

 at Semur show the sudden spreading out by migration of forms of Psiloceras and 

 Schlotheimia from South Germany into the Cote d'Or at about the same time, 

 and a somewhat later appearance of these radicals in the Rhone and North Ger- 

 man basins, and possibly still later in England. It seems more likely also, from 

 the two tables given above, that the species of Schlotheimia, Psiloceras, Caloceras, 

 and perhaps Vermiceras, were migrants from the Cote d'Or basin to the Rhone, 

 than that the reverse should have taken place. Coroniceras also thins out in 

 this direction, whereas the genera having their acme in the upper horizons of the 

 Lower Lias, viz. Asteroceras, Agassiceras, and Oxynoticeras, are more abundantly 

 represented, perhaps, than in the Cote d'Or. All the information obtainable 

 with regard to the faunas of the Lower Lias in Switzerland indicates a general 

 thinning out in numbers of species and varieties in that basin which, like the 

 basin of the Rhone, lies to the south of the autochthonous zone. 



Emerson's collection from Markoldendorf now at Amherst, Mass., and others 

 we have seen, show that the fauna of North Germany was probably derived from 

 South Germany, and this accords with Seebach's conclusion, that a connection 

 existed between the Hanoverian and South German faunas during the time of the 

 deposition of the Lower Jura. 2 There is considerable doubt whether the English 

 species of Psiloceras and Caloceras came by the way of the Cote d'Or, or found 

 this locality by independent migration. The former opinion is supported by the 

 general fact that the English fauna does not contain an autochthonous series, nor 

 does any radical species appear earlier in this basin than in those of the conti- 

 nent ; it is therefore probably a residual fauna, peopled by chorological migration. 

 1 Ann. des Sci. dml.. I. 1S69, p 17".. pi. v. - Hannoverische Jura, p. 70. 



