METAMORPHOSED PUCOID SCHISTS IN SCANDINAVIA. 163 



of the alum slate of Scandinavia ; and I can scarcely doubt that the most cha- 

 racteristic properties of the alum slate as depending upon its carbon, its sul- 

 phur and its potash, are derived from the great quantity of sea-weed which 

 has been mixed up with the clay, and whose carbonaceous matter so affects 

 the whole rock, that the slate is used as fuel for boiling the aluminous liquor, 

 and burning lime, and iu some parts of the province of Westergothland in 

 Sweden even small courses of true coal occur. There can hardly remain any 

 doubt that this coal is derived from sea- weeds of which the fossil parts have 

 been found, for not the slightest trace of land plants has ever been dis- 

 covered*. 



In most parts of Sweden, principally in Westergothland, the aluminous slate, 

 which rests upon a quartzose sandstone, is separated from the upper slates, 

 which are not aluminous, by a large bed of limestone, which contains Asaphus 

 expansiis, Illanus crassicauda^ and numerous Orthoceratites. The aluminous 

 slate contains a vast number of small Trilobites, which are peculiar to it, and 

 might appear at first to prove it a peculiar formation deposited at a time when 

 other animals lived in the sea than those which occur in the overlying lime- 

 stone. In Scania and in Bornholm the aluminous slate and the bed of 

 limestone with Asaphus expansus are merely subordinate beds in the large 

 formation of lower Silurian slates, and of course contemporaneous with them. 

 Notwithstanding, the aluminous slate contains a vast number of the same small 

 Trilobites, and the limestone the same Asaphus expansus which is found in 

 the peculiar beds of Westergothland, thus proving that all these animals have 

 lived at the same time. If we compare the great number of small Crustacea 

 which now live in the sea-weed thrown upon our shores, it appears to me 

 highly probable, that the great number of small Trilobites and Agnosti which 

 are found in the aluminous slate are the representatives of those of our crus- 

 taceans which live upon sea-weed, and that the difference in the fossils of the 

 aluminou's slate, the limestone bed and some of the beds of the clay slate, does 

 not depend upon the difference of time in their formation, but arises from a 

 difference of food in various localities for these animals. 



There is still another difference between the alum slate and the surrounding 

 clay slate ; while the last contains more or less carbonate of lime dispersed 

 through it, the alum slate contains a very small quantity of it. In fact, if alum 

 slate contained lime in any considerable quantity, it would be quite useless 

 in the manufactory of alum, because all the sulphuric acid would combine 

 with lime instead of alumina, and form gypsum instead of alum. If however 

 we consider the whole mass of alum slate, lime is not wanting ; the difference 

 consists only in the circumstance, that the carbonate of lime of the alum slate is 

 collected into large balls or concretions penetrated by bituminous substances, 

 and on that account black and fetid on being rubbed, while it is not so if col- 

 lected in the common clay slate of these regions. It is evident that there must 

 have been some cause or other by which the carbonate of lime was first dis- 



* An objertion might be made, that this cause vvouUl not be sufficient to account for the 

 enormous mass of iron pyrites deposited in the alum slafe, but a calculation will show that this 

 is not the case. At the point of Kronborg near Elsingor, about 30,000 two-horse loads of sea- 

 weed are annually thrown on shore in the months of November and December, which, calculated 

 at 500 lbs. dry plants each, are equal to 15 millions of pounds, which at 3 per cent, sulphuric 

 acid, would make 450,000 lbs. of sulphuric acid and 332,000 lbs. of iron pyrites ; and if we 

 then calculate every solid cubic foot of alum slate at 15 lbs. and the alum slate on an average 

 at 2 per cent pyrites, the quantity of sea-weed annually thrown upon the shore at Kronborg 

 would thus be sufficient to impregnate 111,000 cubic feet of alum slate with pyrites. Besides, 

 I may mention the enormous extent of floating sea-weed in the gulph-stream between Europe 

 and America, as more than sufficient to account for any known quantity of pyrites in sedi- 

 mentary deposits. 



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