M. Keilhaifs Theory of Granite and other Rocks. 393 



so have undoubtedly not nearly such enormous cubic bulk. 

 We have opportunities of observing in many places that they 

 form beds of very great size, upon the stratified transition-rocks, 

 so that they do not descend into these, at least with their 

 whole horizontal extent. In several other respects also, they 

 present different features from the granitic masses. They often 

 exhibit in the form of beds pretty horizontal offsets ; we find in 

 most places, that in the strata lying immediately under them there 

 are no dislocations ; no substantial alterations are observable in 

 the transition-rocks at their junction with the porphyry, and 

 contact minerals at the boundaries are awanting; lastly, it is a 

 remarkable relation of the porphyry, and one which seems to 

 be the result of a very fixed rule, that it reposes only on sand- 

 stone, and thus, in general, can only occur where this mem- 

 ber of the transition group is present: in the Upland territory, 

 which contains this sandstone only at one locality, it is precisely 

 at that place, and there alone, that porphyry is found. But be 

 that as it may, so far as it concerns the part we have for 

 the present assumed in the discussion, we need not be em- 

 barrassed ; we have an all-important fact in reserve, to over- 

 turn every doubt which can be started as to the conclu- 

 sions, that these porphyries have risen up from the interior and 

 have been poured over the beds of sandstone, — that it was so 

 only over the sandstone, may be an accident. This fact is ana- 

 logous to those by which we have strengthened our volcanic 

 faith, viz., the phenomena exhibited in the mutual relations of 

 the trap-rocks and the brown coal-deposit of Iceland.* In the 

 present case, we can ourselves easily be witnesses to the re- 

 markable phenomenon of a trap mass spreading itself out over 

 Neptunian strata in the form of a more or less horizontal bed, 

 and at the same time occurring as a more or less vertical vein 

 in the same strata ; we can observe with tolerable distinctness, 

 the union of the vein with the l)ed-like mass, which, indeed, no 

 one, it would be supposed, can deny, was raised up in a li- 

 quid state through the vein-fissure (gangkloft) proceeding from 

 beneath ! It is in the neighbourhood of Holmestrand that I 

 have observed this appearance, and we have here a true ex- 



• The geological constitution of Iceland appears to me extremely import, 

 ant for the| theory of Trap-rocks. The phenomena mentioned in the text 

 gre described by^KrugJVon Nidda. 



