UNGULITE GRIT OF ST. PETERSBURGH. 
27 * 
The upper strata are yellow and ferruginous, and are surmounted by a bitumi- 
nous schist, which sometimes, indeed, is first seen to alternate with the uppei 
beds of the sandstone, and then distinctly to separate it from the overlying lime- 
stone. 
The rock derives its name from being in parts copiously filled with minute frag- 
ments of the Obolus or Ungulite l , which, from their dark and shining aspects, give 
to it a very remarkable aspect. This peculiar rock, which on the Pulkovka and 
Popofka brooks (the first to the west, the second to the south of Czarskoe-celo) 
is not more than from twelve to twenty feet thick, expands gradually in its course 
both to the east and to the west, until it becomes, in some places, a considerable 
mass. Upon the Ishora 9 and Tosna rivers it is seen to rest upon the lower shale, 
and to be capped by the schist and limestone. Its lower or whiter beds are theie 
laminated with thin courses of shale or impure fuller’s earth, whilst the uppermost 
bed (which there alone contains Ungulites) is highly ferruginous, with a few large 
pebbles of quartz. On the Volkof and Siass rivers, the Ungulite grit is also seen 
reposing upon the blue sbale ; on the former, about two miles below Starai Ladoga, 
on the latter between Pulnitza and Rebrova. On the banks of these rivers the 
sandstone assumes the importance of a distinct formation, and occupies cliffs 
upwards of 100 feet high, the lower portion white, the upper yellow and ferru- 
ginous. 
On the Siass it is composed ol thick bands of an incoherent sandstone which 
weathers to a white colour on the external surface of the cliff, but is of a pinkish 
hue when fractured, and slightly freckled with ferruginous stains. Ihe beds aie 
occasionally separated by thin courses ol shale or clay , and the whole lests distinctly 
upon the blue clay. Occasionally these ferruginous beds become a botryoidal or 
mammillated iron sandstone. 
Near Starai Ladoga on the Volkof, the rock is for the most part a friable, 
incoherent sandstone, though it is probable that if deeply cut into, it might afford 
a tolerable building-material. In its range to the west it is often, indeed, more 
■ This fossil “hell was first described by Eichwald under the name of Obolus, which we retain in our 
description of the organic remains. We use, however, the name of Ungulite grit (so applied by Pander) 
because it has obtained geological currency. The multitude of the small shmmg fragments of this 
horny shell might, at first sight, be mistaken for plates of mica, and we have already adverted to shells of 
similar characters in the oldest Silurian shelly rock in North America. 
* In one spot on the Ishora, as remarked by Strangways, the white sand is so fine that it is extracted 
for hour-glasses and writing purposes. 
