608 [April 30. 



Approacliing the spot in a boat, it was interesting to observe the 

 very gradual and perceptible change, from the unaltered schists and, 



Bagten. Egeberg. 



Greenstone and 

 Palaeozoic gneiss. 



a. Black alum schist passing into chlorite schist and gneiss. 

 h, Lower Silurian rocks. 



flagstones of the low neck of land, to the highly contorted and 

 metamorphosed masses which rise up into the little promontory. 

 The flags and limestone being first contorted and deflected, are 

 succeeded by black alum shale, in which is disseminated a great 

 quantity of iron pyrites mostly in a decomposing state. Gradually 

 this rock, in vertical strata, is seen to pass from the black shale 

 (which is a fine alum schist on the other face of the Egeberg) 

 into greenish micaceous schists, which, as they approach nearer to 

 the mountain, and to the focus of eruptive greenstone, become 

 more and more crystalline, until they might pass for a good pri- 

 mary schist, not easily distinguishable from much of the old gneiss 

 of the adjacent country. In the upper portion of this mass, or 

 that nearest to the black shale, the rock is loaded with little crys- 

 tals of iron pyrites, evidently formed by an aggregation of the 

 loose and scattered particles in the altered shale. In the most 

 crystalline portion, however, or that which is nearest to the bosses 

 of intrusive greenstone, are veins of the crystallised pyrites. A sin- 

 gular feature in this conjunction of appearances is, that long and 

 slender veins of quartz radiate as it were throughout the rocks, 

 traversing the greenstone and mock gneiss, and also passing from 

 that into the black and contorted shale. I have specially described 

 this spot, both because it affords the best evidence with which I 

 am acquainted of the conversion of alum shale into a gneissose 

 rock with chlorite, &c., and because the chemical process followed 

 by nature in operating this change has been admirably explained 

 by Professor Forchhammer, who has endeavoured to show that 

 as no argillaceous schistose rock could undergo similar melting 

 and metamorphosis without the medium of a flux, so there was 

 potash existing in the alum-shale, derived from the decomposition 

 of fucoids, and which, therefore, originally deposited in consider- 

 able masses in the rocks, had served as the flux whereby the 

 whole mass was fused and metamorphosed. 



In referring geologists to the paper by Professor Forchhammer 

 on the conversion of fucoid alum shale into a gneissose rock, pub- 

 lished in the volume for 1844 of the Reports of the British Associa- 

 tion for the Advancement of Science, I ought to state that M. 

 Forchhammer is quite as intimately persuaded as myself, that how- 

 ever such metamorphosis may have been brought about, there is no 

 doubt that the converted palaeozoic rock can never be mistaken, ex- 



