2 
THE GEOLOGIST. 
formation has been found and named ; its rocks and fossils have been 
described ; and the Purbeck beds have returned to their former 
associates — the Jurassic rocks. 
During this period of time several geologists have tried to find the 
marine equivalents of the Purbeck and Wealden rocks, without, 
however, arriving at results satisfactory to all observers. The ques- 
tion is still veiy far from a solution ; but I have lately learned several 
new facts on the subject which perhaps may be of some assistance in 
facilitating a recognition of the marine deposits coeval with the 
Wealden. 
In order that my references and data may be clearly understood, I 
will first give a short description, or resume, of the strata in the Jura 
Mountains comprised between the Portland stone and the Lower 
Greensand. This resume is also graphically presented in the Abstract 
section of the series of strata comprised between the Banne Limestone and 
the Rhodanian group, in the Jura Mountains (PI. I., Fig. 1) — under 
the form of a tabular and proportional view . 
The Jurassic divisions known under the names of Bann6 Limestone 
(Calcaires du Banne) and Salins Marls {Marnes de Salins)* contain a 
fauna identical with that of the Portland beds, with the addition of 
some new species peculiar to the Jura, and a few fossil shells common 
to the Kimmeridge clay. The Salins Marls are succeeded by a series 
of compact limestone strata, very thick (100 feet at least), of a 
whitish-grey, and sometimes clear yellow colour, containing beds of 
lithographic stone a little above the middle of the division, and 
always capped by a sort of magnesian limestone (Dolomite). This 
series, called Salins Limestone [Calcaires de Salins), contains numerous 
fossil remains, all of marine animals, especially Corals, Echinodermata, 
Nerinea, and Natica; two hundred different species at least. The Leit- 
muscheln (guide-shells) are : — Ilemicidaris Furbeckensis, Forb. ; Pygurus 
Jurensis, Agass.; Pinna Barrensis, Biiv. ; Trigonia gibbosa. Sow.; Natica 
Marcousana, D'Orb. ; N. Athleta, D'Orb. ; Rostellaria Barrensis, Buv. ; 
Nerinea Salinensis, D'Orb. ; N. Elea, D'Orb. ; N. subpyramidalis, 
D'Orb. ; N. grandis, Volt. ; N. trinodosa, D'Orb. ; JV. cylindrica, 
* See, for exjilanation of these tenns, Leftres sur ks Roches du Jura et leur 
distribution geoyraphicpie dans les deux HemiipMres, par Jllles Marcoii ; 
Paris, 1857. 
