316 M. Alex. Brongniart sur les caracteres Zoologiques, &c. 
After these general considerations M. B. proceeds to 
the consideration of several anomalous members of the 
chalk formation; all of which he refers to this formation 
from the analogy of their fossils. 
1. Chalk of Rouen, Havre, and Stonfleur. At the mill 
of St. Catharine, near Rouen, the white chalk is found 
overlying the chalk tufa or green sand. The two latter 
contain many fossils not found in the former. At Havre 
and Stonfleur, the white chalk is wanting. The inferior 
chalk is there exactly analogous to that at Beachy Head, 
and Dover, Eng. and at Saugatte, W. of Calais; it is sepa- 
rated at the two last places from the white chalk or tufa, 
there present, by a bed of blue marle. All these locali- 
ties of green sand and tufa are characterized by precisely 
similar fossils, of which M. B. gives a catalogue. 
2. Chalk of the environs of Perigueux. Bayonne. 
‘The chalk of the N. of France terminates at the S. line 
of Indre Dep. Passing S. W. the chalk-tufa re-appears 
near Perigueux, particularly to the westward of that town, 
the high steep hills along the Lille below that city, area 
grey sandy, and often micaceous chalk, without distinct 
strata; but its stratification is marked by beds of black 
hornstone, which divide it into numerous layers. It 
abounds in shells, some of them (ostrea vesicularis,) hike 
the smaller specimens of Meudon. 
Passing south west, other rocks occur referable to the 
chalk formation, where it was not before suspected. Such 
is the hard gray sandy micaceous limestone, which forms 
the basis of the soil around Bayonne, and particularly the 
rocks of Biarite. It contains shells analogous to those 
of the chalk tufa near Paris, particularly the spatargus ob- 
natus. Its stratification can be ascertained only by the 
difference in the solidity of its parts. It is made up of 
alternate zones of a grayish, crumbling, argillaceous, or 
sandy limestone, anda hard limestone, divided into a series 
of irregular nodules, projecting from the escarpments like 
the flints inwhite chalk. It abounds in fragments of shells, 
particularly echinites, but no ammonites. Although many 
of these shells have specific differences, yet their general 
character is that of the chalk formation. 
3. Chalk of Poland, from these localities—white chalk 
like that of Meudon, with black flints and belemnites, 
