1845.] 609 



cept in isolated specimens, for the ancient Norwegian gneiss ; since 

 the former, however much altered, can always be traced without 

 any unconformable junction from the crystalline strata into a 

 slightly altered rock, and then from that into wholly unaltered 

 and fossiliferous Silurian bands. On the other hand, no such 

 example of transition from the great masses of ancient gneiss into 

 Silurian rocks has ever been seen in any part of Scandinavia ; 

 and however an example like this, where the converted rock re- 

 sembles the more ancient gneiss, might tend to mislead a young 

 observei', I shall show in the sequel how these fucoid strata, or 

 oldest Silurian rocks of other parts of Scandinavia, repose on 

 previously formed gneissose rocks. 



If some geologists should contend, that as fucoids are compara- 

 tively of rare occurrence in strata, the theory of Professor Forch- 

 hammer is not based on adequate data to account for more than a 

 partial phonomenon, I beg entirely to dissent from such scepticism. 

 No one can ever have looked at the forests of alg^e and fuci which 

 are living in many sea bottoms (and I was powerfully struck 

 with their profusion in the deep and clear fjords of Norway), 

 or have reflected on the enormous bands of such vegetables 

 which extend thi'ough many degrees of latitude, as described 

 by Mr. Lyell, without admitting that many, if not by far the 

 greater portion of our sea-formed strata, which now constitute the 

 chief masses of our continents, may have originally contained 

 fucoids, although, from their ready decomposition, and the great 

 changes which the sediments have undergone, distinct evidences 

 of their existence are comparatively seldom to be met with. And, 

 as in huge masses of the fucoid schists of Scandinavia, where the 

 form of the vegetable has disappeared, the rock is only distin- 

 guished either by its anthracitic or bituminous qualities (parts of 

 it being sometimes so carbonaceous as to be used as fuel for roast- 

 ing the other portions of the alum slate), so I can very well 

 conceive how many of the schists and slates of England, from the 

 loAver Silurian to the Lias and superior rocks inclusive, have 

 derived their pyritous, aluminiferous, and often inflammable pro- 

 perties from the ancient diffiision therein of a large proportion of 

 fucoids. The very seas in which the azoic rocks themselves were 

 formed may in like manner have contained abundance of fucoids, 

 whose decomposition may have afforded a flux for the metamor- 

 phism of those the most ancient deposits in the crust of the globe. 



Passing, however, from these theoretical considerations, I will 

 now merely add, that besides the case observed at the foot of the 

 Egeberg, I also remarked what I conceive to be similar phenomena 

 in the cliff* on which the Agershuus, or fortress of Christiania 

 is built. M. Von Buch directed my attention to what he con- 

 sidered to be an anomaly in the appearance of that singular 

 outlier which is separated from the main mass of gneiss by a 

 broad trough of Silurian schists and flagstones on which the 

 town and environs stand. On examining the seaward face of 

 this promontory, I found it to be also composed of black schists 



