114 GENESIS OF THE ARIETIDA. 
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 Infra 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 basin of the Mediterranean possesses a series of beds identified as belonging 
to the zone of Avicula contorta, but there are no Ammonitinee, 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. 
Kmerson’s collection from Markoidendorf 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.? 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. Géol., I. 1869, p. 473, pl. v. 2 Hannoverische Jura, p. 70. 
ea 
