1845. J 613 



to the south of Wadstena, among other phenomena of gieat interest, 

 we found that along the steep shores of the Omberg, one of the 

 few hills in Southern Sweden where the granitic gneiss occupies 

 a tract of any considerable 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. 



The Orthoceratite limestone is largely quarried at the village of 

 Borghamm, near the northern end of the Omberg ; but by coasting 

 that mountain iil 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 occur in nearly vertical positions, plastered as it were 

 against the great wall of crystalline rock. Still further on, or 

 southwards, the chief mass of granitic gneiss retires somewhat 

 inland, laying open coombs 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. The inclined strata are chiefly composed 

 of soft argillaceous shale entirely unaltered, even when they are 

 in absolute 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. Across the 

 edges of one group only of these beds near their southern ex- 

 tremity, where the mass of the granitic rocks retires inland, and 

 which are inclined at about 35° to the north for upwards of 800 

 paces, their lower part consisting of black shale (alum-slate) 

 wholly unaltered, we came to the lower fucoid sandstone. Here 

 again there could be no misgivings ; for this sandstone having been 

 considerably eroded and worn away by the stormy action of the 

 waters of the lake, the lower granitic gneiss beneath it has been 

 exposed as a nucleus, around which the white, sandy and regene- 

 rated sandstone has been wrapped, and is still in a wholly un- 

 altered state ! 



These facts completely demonstrate what we are contending for, 

 that the granitic gneiss and associated rocks of Sweden formed the 

 solid materials of that country before the earliest A^estiges of 

 palaBozoic deposits were called into existence. They further prove, 

 that as the Lower Silurian strata in question which are actually 

 adherent to the granitic rocks, though highly dislocated, occur in 

 the state of soft shale and unaltered impure limestone and sand- 

 stone, the crystalline ridge of the Omberg must have been up- 

 heaved as a hard and solidified mass, long after the period when it 

 had undergone the fusion and metamorphism which gave to these 

 ancient slaty rocks their crystalline aspect. . 



Other phenomena, proving that the lowest Silurian sandstone 

 of these tracts has been formed out of the ancient crystalline 



z z 2 



