SUPPLEMENTARY NOTES. 
613 
in the same category with the fossil calcareous exuviee oi Fora- 
minifers, Polypes and Crustaceans. 
The living species of these animalcules, which are now be¬ 
ginning to be found so abundantly in a fossil state, are divided 
into two classes and six families; three of these families have a 
naked flexible epidermis, and three, a siliceous epidermis, forming 
a transparent shell, or cuirass. The cuirass, in the greater 
number of species, is composed of two siliceous valves, the uni¬ 
valve cuirass has the shape of a leaf, with its edges rolled in¬ 
wards towards each other. About one half of Ehrenberg’s genera 
of Infusoria, have a siliceous cuirass, and the other half, a 
membranous covering. 
The species found at Carlsbad do not live in the rising thermal 
water, but are seen at a small distance from the spring, covering 
the stones and wood with a green slimy substance, chiefly com¬ 
posed of the bodies of millions of Infusoria. These animalcules 
are never found in the rising water of a hot spring, nor in 
the limpid water of a cold spring, river, or well. 
P. 448, Note. Mr. SearlesWood has discovered fifty species 
of foraminifers in the lower Crag formation of Suffolk. 
Lond. and Edin. Phil. Mag. Aug. 1835. p. 86. 
P. 495,1. 4. Mr. Webster was the first who noticed in the I. of 
Portland the interesting Phenomena of the Bed of black vegetable 
mould called the Dirt Bed , with its fossil wood, pebbles, &c. and 
ascertained that the silicified Trees found in this island had been 
obtained from this bed only, and not from the Portland Oolite. 
Geol. Trans. Lond. N. S. Vol. II. p. 42. He also states that 
the Purbeck series contains strata of Fresh-water origin, and 
is thus distinguished from the Portland Oolite, which contains 
marine shells only. In the Paper referred to, he hesitates where 
to draw the exact line of separation between these two forma¬ 
tions, but is inclined to place it at the Chert Bed, (See PI. 57, 
Fig. 1.) an opinion which he still maintains. In the same Paper 
he considers the Dirt Bed not to rest immediately upon a stratum 
of marine formation, (as Mr. De la Beche and myself have subse¬ 
quently and erroneously supposed it to do; Geol. Trans. N. S. 
