168 



REPORT 1844. 



has lost almost the whole quantity of water which it contained. It seems 

 evident that this change has been brought about by the very numerous trap- 

 paean and euritic dykes which traverse these shales. 



The second state in the change of the alum slate is into Lydian stone; this 

 occurs at Bugten, near the sea-shore at the foot of the Egebei-g, about a couple 

 of English miles to the south of Christiania ; it is black, hard, and traversed 

 by numerous small veins of quartz, which seem to depend upon the protrusion 

 of large irregular masses of greenstone. 



The third stage is into a gneissose rock witli a quantity of dark mica and 

 black scales of a carbonaceous substance, which seems to be graphite. This 

 variety Mr. Murchison also observed at Agersberg Castle, in the town of 

 Christiania itself. It being a matter of great importance to ascertain whether 

 this completely gneissose rock still contained carbon, I have made two experi- 

 ments to convince me of this fact. I made an analysis like those for organic 

 substances, and ascertained the quantity of carbonic acid, -which gave the 

 quantity of carbon as 1-28 per cent. Since there might, however, remain 

 some doubt, whether a minute portion of the carbonic acid might not depend 

 upon a small quantity of carbonate of lime that occurred in this rock, I dis- 

 solved a portion of it in a mixture of fluoric and muriatic acid, whereby a 

 quantity of finely-divided carbon remained, which, after being dried, burnt 

 on a red-hot piece of platina with the phaenomena of burning carbon. It is 

 thus completely proved that the black gneissose rock of Agersberg still con- 

 tains a quantity of carbon. This carbonaceous gneiss is wanting at Bugten, 

 where the series is generally more perfectly displayed. 



Next to the layers of Lydian stone of Bugten a gneiss makes its appear- 

 ance, consisting of dark green mica, white felspar, quartz, and a number of 

 small cubes of iron pyrites disseminated throughout the mass. Of this most 

 perfect gneiss (which on the place itself, however, is very closely connected 

 Avith Lydian stone, and whose pyrites still show its origin from the pyritiferous 

 alum slate) I made a complete analysis, the result of which, compared to the 

 analysis of the alum slate of Bornholm and Opsloe, is the following ; the water 

 and carbon of the alum slate having been deducted before the per-centage 

 was calculated : — 



1. 2. 3. 4. 



Alum slate from 

 Opsloe, after de- 

 duction of the 



volatile parts. 



. 72-40 . 



. 16-4.5 . 



. 2-26 



. 0-17 



. 1-48 



. 5-08 



. 0-53 



. 1-25 



Gneiss from 

 Bugten. 



Alum slate from 

 Bornholm. 



Silica .... 

 Alumina . . . 

 Peroxide of iron 

 Lime .... 

 Magnesia . . 

 Potash . . . 

 Soda .... 

 Sulphur . . . 



69-71 

 13-59 

 7-77 

 0-23 

 2-65 

 3-79 

 0-46 

 2-30 



Alum slate from 

 Bornholm. 



. . 71-72 



71-72 . . 

 . . 19-04 



Pyrites 1-58 Oxide of iron 9-06 

 . . 1-19 



2-02 



4-46 



traces 



Sulphur 4*15 



100-68 99-62 99-87 



In analyses 1 , 2 and 4, the quantity of oxygen corresponding to the quantity 

 of sulphur which was found must be deducted, because a portion of iron is 

 present as pyrites. In No. 4 only the quantity of silica, oxide of iron, and 

 sulphur was determined, and their quantity given proportionally to the silica 

 in No. 3. 



If Ave compare these analyses, the close connexion of the rocks analysed 



