FORMATION OF NORTHERN GERMANY. 117 
ness, of pure white carbonate of lime, inclosing seams and bands 
of flints in intermediate layers, and in oblique or vertical fissures. 
The carbonate of lime is compact, or has an earthy fracture ; 
adheres more or less to the tongue; is generally of a pure white 
colour; sometimes it is soft, as for instance in the writing chalk, 
at other times somewhat harder; and it is so free from foreign 
constituents that scarcely 0-006 silica is found in it. This in 
some cases is accompanied by a little iron, which imparts to it a 
grayish colour. The specific gravity is about 2°34. 
The single layers are from 1 to 4 feet in thickness, and are 
generally much rifted. 
Numerous seams of flints, from a few inches to some feet in 
thickness, alternate with the calcareous beds. The flints have a 
specific gravity of 2°594, and contain, according to Klaproth’s 
analysis,— 
eae ra ts ee De FOR 
Carbonate oflime . .. . . . 0:005 
Pera Be SE EY eS OONER 
Oxide of iron (eisen oxyd) . . . 00025 
PCEGCER IMG? oa 8.SoGn SN Od 
In the interior, the colour of the flints varies between gray and 
black ; they possess a conchoidal fracture and a faint lustre, are 
translucent at the edges, and sometimes include cavities par- 
tially filled with chalcedony and crystals of pure quartz; by ex- 
posure to the air their colour gradually becomes yellowish ; and 
in the fire whitish and quite opake. Very frequently minute, 
well-preserved corals are found in them, which perhaps may 
alone have effected the separation of the acid of silica*. 
The flints form roundish irregular nodules, frequently flat- 
tened, and varying in size from that of a fist to several feet in 
diameter: they lie close together, seldom however in contact, and 
are commonly surrounded by the chalk; their surface, which 
consists of a combination of lime and silica, is whitish, rough 
and harsh to the touch. These flints frequently form only hori- 
zontal seams, but sometimes numerous ranges of them (schniire) 
are met with, traversing the other strata in a perpendicular or 
inclined direction. 
Of other minerals there occur calcareous spar, chalcedony, 
crystals of quartz, and iron pyrites. The calcareous spar fre- 
* Welche die aussonderung der kieselsdure allein bewerkt haben (Orig.). 
