17 
SECTION ALONG THE OMBERG. 
height, the relations of the Lower Silurian strata are, if possible, still more strongly 
indicative of their having been derived from the adjacent pre-existing crystalline 
rocks. Details of these features would he here misplaced, and we shall therefore 
offer a few words only upon them. 
The Orthoceratite limestone is largely quarried at the village of Borghamm, near 
the northern end of the Omberg ; but by coasting that mountain in a boat along 
its western face, the granitic rock of which it is composed, is seen to occupy the 
whole surface for some distance, in cliffs rising to 400 or 500 feet above the lake. 
In about a mile, however, broken masses of the Lower Silurian rocks (6 and c) 
occur in nearly vertical positions, plastered as it were against the great wall of 
crystalline rock (o), as represented in this sectional drawing. Still further on, or 
THE OMBERG. 2*. 
N. S. 
Mulskrederna (a great fall of rock.) 
southwards, the chief mass of granitic gneiss retires somewhat inland, laying open 
combs upon its inclined surface, and in these are very considerable masses of Lower 
Silurian strata with an occasional Orthoceratite, but with little calcareous matter 
and few fossils. These strata occupy a considerable thickness, both in a slightly 
inclined, almost horizontal terrace, and also in vertical and highly inclined positions, 
as represented in the above woodcut. The inclined strata ( b and c ) are chiefly 
composed of soft argillaceous shale entirely unaltered, even when they are in abso- 
lute contact with the granitic rocks, and in them, and also in certain alternating 
courses of calcareous grit, are many included small pebbles and fragments of the 
crystalline rock. Pacing across the edges of one group only of these beds near 
their southern extremity, where the mass of the granitic rocks retires inland, and 
which, as above exhibited (towards the right-hand of section), are inclined at about 
35° to the north for upwards of 800 paces, their lower part ( b ) consisting of black 
shale (alum-slate) wholly unaltered, we came to the lower fucoid sandstone (a). 
Here again there could be no misgivings ; for this sandstone having been consi- 
derably eroded and worn away by the stormy action of the waters of the lake, the 
lower granitic gneiss beneath it (o) has been exposed as a nucleus, around which the 
white, sandy and regenerated sandstone (a, a) has been wrapped, and is still in a 
wholly unaltered state. 
