396 Linnarsson — On the Eopkyton Sandstone. 



On geognostical as well as upon palaeontological grounds two 

 divisions may be distinguished in the sandstone of Vestrogothia. 

 In the lower, which is seldom seen in any natural section, the rock is 

 hard, usually thin-bedded ; in the upper, which is in many places 

 exposed and has chiefly given rise to the names of Fucoid sandstone 

 and regio Fucoidarum, it is softer and often thick-bedded. At the 

 very limits of the adjoining layers the sandstone is of an anomalous 

 composition. At the limit of the gneiss it has the appearance of a 

 conglomerate, and contains also some felspar grains. The uppermost 

 sandstone which lies immediately beneath the lowest alum-slate con- 

 tains a great deal of pyrites, and sometimes, as at Hunneberg, of 

 clay also. These anomalous portions of the layer are very thin, 

 being hardly more than one or two feet in thickness. 



The lower parts of the sandstone, although not overlooked by 

 earlier writers, have, owing mainly to the researches of Dr. Wallin 

 and to Professor Torell's descriptions of the fossils collected by the 

 former, attracted a greater degree of attention, and it was through 

 their works that I was led to make myself acquainted with them. 



The Lugnas^ mountain offers the best opportunity of observing 

 the lower division of the sandstone layer and its contact with the 

 underlying gneiss, that is to say, the line of demarcation between the 

 Cambrian and the Laurentian systems. For that reason this locality 

 has often been visited by geologists, but their views respecting the 

 position of the limit are very different. From the olden time mill- 

 stones have been quarried on a large scale in many places at the foot 

 of the mountain, out of a rock containing the ingredients of granite 

 and gneiss, but in which the felspar has partially been converted 

 into kaolin. According to some writers, this rock is a weathered 

 granite or gneiss, and as such referred to the Laurentian system, or 

 the " fundamental rocks ; " others have believed it to be an arkose 

 formed by the mechanical decomposition of a granitic or gneissose 

 rock and the subsequent cementation of the components. According 

 to this opinion it would constitute the lowest portion of the sand- 

 stone, and thus belong, together with the overlying sandstone, 

 to the Cambrian (respectively Silurian) system, or the lowest part of 

 the " Transition formation." Hisinger hesitates between these two 

 opinions ; sometimes he names the rock a " rotting " granite or 

 gneiss,^ but sometimes he says that " the millstone bed may be per- 

 haps properly regarded as a granitic transition arkose separated from 

 the fundamental rock or the gneiss by a thin quartzose layer." ^ Sir 

 Eoderick Murchison believes the rock to be a Silurian arkose, con- 

 stituting the lowest part of the sandstone.* But Dr. Wallin, in 

 his detailed and accurate description of the layers of the Lugnas 

 mountain,^ has clearly shown, that the millstone rock is nothing but 

 a variety of the common gneiss of the district, caused by the partial 



^ Pronounce : Lungnose. 



2 Anteckningar i Physik och Geognosi, Vol. It. p. 48, 49 (1828). 



3 Anteckningar, Vol. v. p. 67 (1831). 



* Eussia in Europe, etc., vol i. p. 16.* Siluria, 4th ed., p. 347. 



* Bidrag till kannedomen om Vestgotabergens byggnad. Lund, 1868. 



