26 GASTEROPODA OF THE INFERIOR OOLITE. 
Derats oF THE Dorset-Somersut District (No. 1). 
The Mendip axis serves approximately as the northern boundary. 
Comparison with Normandy. 
There can be very little doubt that both the Upper Lias and the Inferior Oolite 
of Dorsetshire present considerable analogies with beds of the same age in Normandy. 
This, indeed, has been pointed out by Oppel and Waagen, the latter of whom 
included Dorsetshire in the Parisian basin as distinct from the Inferior Oolite of 
the whole of the rest of England. 
As regards the Upper Lias we have only to compare the general section at 
Ilminster, given by the late Charles Moore,’ F.G.S., with the section at Evrécy, 
given by Prof. Hugtne Deslongchamps’ to perceive that above the margaritatus-beds 
(Marlstone), there come the Leptena-beds, and then that remarkable zone of nodules, 
or doggers, with Saurians, Fish, and Crustacea, succeeded by certain beds con- 
taining Cephalopoda characteristic either of the Upper Lias proper, or of the 
insignis-zone. At Ilminster the whole of this, judging from the above-quoted 
section, is contained in about eight feet six inches, whilst at Evrécy the thickness 
of the corresponding beds does not exceed thirteen feet. But now supervenes an 
element of great physical difference in the Yeovil sands, over 100 feet thick, which 
separate the bifrons-beds from the regular Inferior Oolite of Dorsetshire. It is 
not a little singular that, whilst the life-zones remain almost identical in the two 
countries, there should be no adequate physical representative of these Yeovil 
Sands in the Department of Calvados. 
But whilst the life-zones present such a singular resemblance, their arrangement 
and classification have been by no means uniform. Let us consult the work of 
Deslongchamps already quoted, in order to see how variously the Inferior Oolite 
may be divided or subtracted from according to the views of various authors. The 
learned Professor of Caen then wrote that the ‘‘ systeme odlithique inférieur ” con- 
sists of (1) Infra-oolitic Marls, (2) Inferior Oolite, (3) Fuller’s Harth, (4) Great 
Oolite. His systeme odlithique inférieur is in fact the equivalent of the whole of 
our Lower Oolites plus the Upper Lias. I have drawn attention to the point 
mainly in order to show the development of the lower portion of the Inferior Oolite 
in Normandy, and its attachment to the Upper Lias, according to certain views. 
For this purpose it will be necessary to analyse the ‘ Infra-oolitic Marls” to see 
1 «Proe. Som. Arch. and Nat. Hist. Soe.,’ vol. xiii (1865-6). 
2 «Etudes sur les étages jurass. inf.,’ p. 75, 1864. 
