184-6.] MURCHISON ON THE GEOLOGY OF GOTHLAND. 31 



In concluding this sketch of the islands of Gothland and Cland I 

 may be permitted to say, that in a region where the strata deviate 

 so very slightly from horizontality, there can be no surer indications 

 of the general strike or direction, than the geographical outlines of 

 the rock-masses and the successive outcrops on a great scale of their 

 different beds. Thus, we see that the major axes of both islands* 

 are nearly parallel and trend from N.N.E. to S.S.W. ; a direction 

 which coincides with the prevalent strike of rocks of similar age in 

 Norway and Sweden, and is to a great extent that which prevails in 

 the Silurian and older strata of Britain. 



In Oland the low sandstone or base rock is only visible in the cliffs 

 on the shore of the N.W. face of the island; it then disappears under 

 the alum shale near Borgholm, and is no longer traceable along the 

 western shore between that point and its southern extremity ; whilst 

 according to Hisinger the alum shale vanishes in its turn near the 

 southern extremity ; the extreme headland being exclusively occupied 

 by the Orthoceratite limestone. These facts show, that whilst the 

 island extends from N.N.E. and S.S.W., its strata subside obliquely 

 to its general outline, and hence that their true strike is probably 

 somewhat nearer to N.E. and S.W. and their inclination on the whole 

 to the S.E. or S.S.E.f 



Assuming that the Orthoceratite limestone of Oland was succeeded 

 l)y schists with Graptolites (as it is in many parts of the mainland 

 of Sweden), there are fair grounds for supposing, that the channel 

 of the Baltic which separates Oland from Gothland has been exca- 

 vated in that soft deposit which would be represented by the letter 

 (d) in the general ascending section. Extending thence our view to 

 Gothland, we perceive that its boldest and highest cliffs (forming its 

 north-western shores) are very nearly parallel to the axis of Oland 

 and consist of Wenlock limestone resting upon shale ; and that these 

 rocks occupying a great area in the northern part of the island, are 

 succeeded by younger strata representing on the whole the Ludlow 

 formation. An ascending order from N.N.W. to S.S.E. prevails 

 therefore in the Upper Silurian of Gothland as in the Lower Silurian 

 of Oland, and the inferences I have drawn from the positive evidences 

 of fossils and lithological changes in Gothland, are sustained by the 

 analogy of the physical arrangements of the inferior strata in Oland 

 which contain well-known Lower Silurian types. 



This view is, indeed, quite in accordance with an opinion I have 

 for some time entertained J, that the Baltic Sea may be considered 

 a great Silurian trough, the lower rocks of which occupy both the 

 Russian and Swedish mainlands, whilst the true Upper Silurian strata 



* See any geographical map ; or the general geological map in the work, 'Russia 

 and the Ural Mountains.' 



t In referring to Forsell's map of Sweden, it will be seen that it is precisely 

 along the bluff chif coast, i. e. the N.N.W. part of the island, that the sea is 

 deepest, and the shore most swept of detritus, and that where the coast is lower 

 and shelves away into sandy and gravelly bays (as around most of the remainder 

 of the island), detrital accumulations are greater and the soundings shallower. 

 This fact seems to strengthen the view of a geological succession from older and 

 more elevated strata on the north and N.N.W., to younger on the south and S.S.E. 



X See Russia and the Ural Mountains, vol. i. pp. 18*, 35*. 



