1845.] 611 



which are subordinate and confined to the azoic rocks strictly so 

 called. The latter, therefore, on the same principle, I would term 

 * Azo-plutonic' In the construction of geological maps, there must, 

 I conceive, be an adherence to the principle embodied in these 

 names, if we desire to mark chronologically the changes which 

 have affected the earth at successive periods. The necessity of 

 this distinction between the older and more recent granites will be 

 made still more manifest when I have described their relations in 

 Sweden. 



Silurian Hocks of Sweden, and their Relation to the older Crys- 

 talline Mocks* — In this notice it will be convenient first to 

 describe the relations of the lower Silurian group to the subjacent 

 crystalline rocks, and then say a few words concerning the fossils 

 of the upper Silurian group of Gothland. 



In the Hills of HoUaberg and Hunneberg to the east of the Falls 

 of TroUhsetten, which are covered by a thick mass of basaltic 

 greenstone, one subordinate member only of the Silurian series is 

 visible, namely, the alum-slate; but no one who knows from nume- 

 rous other sections that this band is very near the Silurian base, can 

 glance his eye over the lower adjacent lands, all composed of 

 gneiss and granitic rocks, or look up from the latter as they appear 

 on the banks of the river, near the Falls of Trollhaetten, without 

 being convinced that the horizontal band of black schistose 

 Silurian rock lies high above the crystalline granitic rocks of the 

 low country, though the absolute junction of the two is hidden by 

 a talus of detritus. 



Advancing to the next Silurian oasis at Kinnekulle and the 

 hills of Billingen, the same general relations of a low surrounding 

 country of gneiss and granite, to high tabular plateaux of hori- 

 zontal Silurian strata, usually capped by trap, present them- 

 selves to the traveller. In ascending the hills of Kinnekulle, from 

 the low gneissose country of Lidkoping, he is no sooner above the 

 low level of those crystalline rocks, than he meets with a terrace 

 composed of quartzose sandstone, already mentioned as frequently 

 forming the lowest Silurian stratum in Scandinavia. This rock, 

 here arranged in beds from a few inches to a foot and a half thick, 

 is light-grey, whitish and fine-grained, in parts freckled with 

 ferruginous stains, and assumes at intervals a quartzose. character, 

 with divisions of chloritic shale. Its lowest beds, or those which, 

 as we shall presently show, rest upon the adjacent gneiss of the 

 valleys, are not here visible, owing to a talus of detritus, but in 

 those which are visible, were found branching fucoid-like bodies. 

 This sandstone is, in fact, seen to constitute the prevalent base of 

 all the Silurian strata, and in the hill of Kinnekulle is surmounted, 

 first, by the black alum schists and limestone ; next by red Or» 

 thoceratite limestone ; and, lastly, by Graptolite schists with some 

 calcareous courses and Orthoceratites. Though irregularly de- 

 nuded over a very considerable area, the Orthoceratite limestone 



* See " Russia and the Ural Mountains," &c., ante cit. p. 15. 

 VOL. IV. PART III. Z Z 



