METAMORPHOSED FUCOID SCHISTS IN SCANDINAVIA. 169 



cannot escape observation ; — the same quantity of silica, magnesia, lime, 

 potash and soda, and only a difference in the quantity of alumina, iron and 

 sulphur, the alumina occurring in a less quantity in the gneiss, while iron and 

 sulphur occur in a much greater quantity than in the common alum slate. 

 But then the sulphur and iron in the alum slate are very irregularly distri- 

 buted, and beds occur which are very rich in iron pyrites ; the bed No, 4, 

 which has been analysed in No. 4, containing even more sulphur than the 

 gneiss from Bugten. The quantity of sulphur must in part depend upon the 

 quantity of iron in the clay which had acted upon the sulphuret of potassium. 

 The great quantity of dark green mica in the gneiss depends upon the presence 

 of oxide of iron, besides the pyrites ; and on looking at No. 4, it is the same 

 case in this alum slate. 



I could not trace any distinct boundary between this gneiss of Bugten and 

 the large mass of gneiss which forms the principal range of the Egeberg ; and 

 near the church of Opsloe one may pursue a similar change in the nature of 

 the rock, although the passage from the alum slate to the gneiss is not as 

 clearly to be traced as at Bugten. 



At both places these changes of the alum slate are connected with large 

 intruding masses of greenstone which irregularly rise from below. Numerous 

 small veins of quartz likewise pass through all the different varieties of the 

 altered rock, from the complete gneiss to the black Lydian stone. 



At the Egeberg near Opsloe, euritic dykes traverse the altered rocks, and 

 these dykes afford a new proof of the peculiar nature of the gneiss which they 

 pass. They have the general chemical character of the intruding euritic rocks 

 of Scandinavia, their alkalies consisting for a great part of soda ; while the 

 newer metamorphic gneiss of Egeberg, like its parent the alum slate, contains 

 a trace of soda only in its composition. 



The older gneiss*, like that of Bornholm, which lies unconformably below 

 the lowest Silurian sandstone and alum slate, contains likewise a considerable 

 quantity of soda in its composition. 



* Note by Mr. MurcMson. — My friend Professor Forchhammer having entrusted this most 

 important paper to my care, I was highly gratified to find, that on being read at York it eli- 

 cited a warm encomium from Professor Liebig, so eminently qualified to form a correct judg- 

 ment of its chemical value. In its very remarkable application to geology I beg to caution 

 the reader against the adoption of the idea, that Professor Forchhammer does not make a 

 clear geological distinction between the newer gneiss and the older. He is indeed entirely of 

 my own opinion, which will be developed in a memoir laid before the Geological Society of 

 London, that the old granitic gneiss of Scandinavia was formed, crystallized and penetrated 

 by granite before the lower Silurian strata were accumulated. — R. I. M. 



