On the Cambrian and Silurian Rochs of Scandinavia. 375 



Silurian rocks in Scandinavia : — (1) Dalecarlia, (2) Ostrogothia and 

 "VTestrogothia, (3) Christiania, (4) Scania, (5) Baltic Isles. A sketch 

 of the stratigraphy of each of these regions was given, and the author 

 drew the following conclusions : — 



. f Mudstones of Bamsasa and Bjersjolagard . . = Ludlow. 

 § | Cardiola beds ; Cyrtograjptus and Retiolites 



'% ■< Shales = Wenlock. 



•■jj Lohiferus Shales; Upper part of Brachia- 

 ls pod beds =May Hill. 



§ f Lower part of Brachiopod beds = Upper Bala. 



'S J Trinucleus Shales ; Beyrichii Limestone . . = Middle Bala. 

 3 J Kargarde Shales ; Cystidean Limestone . . = Lower Bala. 

 £ [ &c. &c. = &c. 



A correlation with the beds of Bohemia was also given. The author 

 pointed out that there is evidence of a physical break (varying in 

 amount), as well as of a palaeontological one, between the Cambrian 

 and Silurian of Scandinavia. Several of the beds of Scandinavia 

 admit of a very exact parallel with strata in the English Lake 

 district. 



The author considered that the fauna of these Scandinavian depo- 

 sits affords evidence of migrations. This can be shown by observing 

 that the same forms occur in two beds of different age, but are 

 absent from an intermediate one ; or by tracing beds laterally, and 

 showing that the forms occur in an earlier deposit in one locality 

 than in another. 



The author considered the black shales deep-water deposits, and 

 accounted for their wide extent by supposing the material derived 

 directly from the decomposition of the felspar in metamorphic rocks, 

 and so in a very fine state of division. The deep-water fauna in 

 the Cambrian appears to have migrated from the south-west ; the 

 shallow-water forms, as might be expected, were more variable in 

 their direction of migration : examples were given in support of this 

 view. In Silurian times the direction of migration appears to have 

 changed, the dispersal taking place from Britain, owing probably to 

 greater local upheaval there. The coast-line also, instead of running 

 in a "W.N.TV". and E.S.E. direction, seems to have run more "W.S.JW". 

 to E.N.E., as shallow-water forms are common in Britain, but deep- 

 water forms in the central Swedish area. The result of the author's 

 investigations, as bearing on classification, is that there is a break 

 in Scandinavia at the base of the equivalents of the May-Hill series, 

 but no other break in the Cambrian series of Sedgwick of equal im- 

 portance — no break, physical or palaeontological, existing at the 

 base of the Ceratopyge limestone (Tremadoc), where some authors 

 have drawn a boundary. 



