SCHEERER — LIMESTONE IN CRYSTALLINE SCHISTS. O 



The most important part of M. Delesse's observations is necessarily 

 the history of the origin and local disposition of the accessory (or 

 rather non-accessory) minerals, the presence of which is in the first 

 place owing to the contact of the gneiss and the limestone*. Gneiss 

 and limestone (regarded merely as chemical bodies, not with respect 

 to their lithological character) have once, it appears, existed vdthout 

 the minerals at present included within them ; and a series of geological 

 events, accompanied by chemical action, has developed the latter 

 within them, and more or less out of them. Both rocks, as they are 

 now presented to us with their included foreign minerals, represent 

 the last stage only of a series of geological and chemical operations, 

 whilst the other stages belong to earlier epochs in the history of their 

 formation, and as far as we are concerned are lost. The investigation 

 of the whole series of phsenomena would be frustrated by an attempt 

 at a too particular enumeration of the several stages, unless we call 

 Analogy to our aid, by which our conclusions may be pushed into 

 apparently inaccessible regions. In applying this to the case before 

 us, we shall have to direct our attention to the limestone occurring 

 under similar conditions in later formations, and not confine ourselves 

 to the consideration of the limestone in the gneiss ; and this especially 

 holds good with respect to the Norwegian phsenomena. 



Since I am to act as guide in this geological excursion, I must pre- 

 mise, that, from the length of time since my visit to Norway, many 

 things have escaped me that may have been of importance for our 

 purpose, and that the deficiency is only partially repaired by memo- 

 randa from my old note-books. 



To some it may appear superfluous to carry on inquiries still further 

 on the origin of crystalline limestones and the rocks in which they are 

 included, as so many distinguished naturalists have already given us 

 the result of their observations on this subject. Still it appears to 

 me judicious, from a non-neptunian point of view, to make advances 

 against ultra-neptunism, lately again rampant. 



If we take a glance at Keilhau's map of the transition district of 

 Christiania f , we shall see that fossiliferous clay-slate is the chief 

 member of the stratified deposits here, for the most part conformable, 

 and traversed by numerous bands of limestone. The chief feature 

 observable here, viz. the sporadic occurrence of a limestone formation 

 subordinate to the clay-slate, is still more plainly seen if we study the 

 phsenomena from place to place in detail. In nearly every hand- 

 specimen of the Christiania clay-slate a more or less considerable 

 quantity of carbonate of lime J is observable. Limestone beds, of the 

 thickness of a few inches and upwards, alternate with clay-slate beds, 

 the latter generally of greater thickness. The smaller of these lime- 



* With regard to the local distribution of these minerals, conditions presenting 

 so many interesting details and therefore not to be treated of in a mere sketch, I 

 must for the most part refer to M. Delesse's original memoirs in the ' Annales des 

 Mines.' 



t Gsea Norvegica, Heft 1. 



t Usually mixed with some carbonate of magnesia. Carbonate of iron is also 

 present. 



c2 



