146 STRATIGRAPHICAL GEOLOGY 



are a series of volcanic rocks porphyritic lavas with massive 

 beds of ash and agglomerate, which seem to occupy the place of the 

 Arenig Series of Wales. 



The groups D 1 and 2 represent the Llanvirn Series, and 

 might be called the Placoparia Beds. D 3 occupies the place of 

 the Llandilo Series, though it is only a thin band, and part if not 

 the whole of D 4 is probably of the same age, but D 5 is 

 undoubtedly the equivalent of our Bala Series ; its highest portion, 

 however, seems to have been removed by erosion before the 

 deposition of the Silurian. 



5. Scandinavia 



When we pass from Central to Northern Europe we come to a 

 region which was evidently at a considerable distance from the 

 contemporaneous lands and continents, and we find that sedimenta- 

 tion was confined to deposits of limestone and shale. Some 

 geologists have too hastily inferred that these deposits are formed 

 under a great depth of water, but the facts do not warrant such a 

 conclusion, only pointing to the existence of an open sea far away 

 from continental land and favourable for the formation of shelly 

 and crinoidal limestones. It was, however, clearly traversed by 

 currents which carried a certain amount of fine argillaceous 

 sediment, and this in some areas completely prevented the con- 

 tinuous formation of limestones. 



In Norway Ordovician rocks are believed to occupy con- 

 siderable areas, but in most places they are more or less meta- 

 morphosed into schists and are plicated with similarly altered 

 Cambrian and Silurian rocks, so that their stratigraphy is difficult 

 to unravel. It is only in the south around Christiania (see the 

 map, Fig. 10) that an undisturbed sequence is found. 



In the south of Sweden also there are several tracts (marked 

 on Fig. 10) where a similar succession can be studied ; the chief 

 of these are (1) Dalarne, north-west of Stockholm ; (2) Nerike, 

 west of Stockholm ; (3) in the Gothlands, on each side of Lake 

 Vettern ; (4) in Skima, the most southerly part of Sweden ; 

 and (5) in the islands of Oland and Gottland (Visby), in the 

 Baltic. 



Within this area also the succession varies, large portions which 

 consist of graptolitic shales in the west and south being replaced 

 by limestones towards the east, and also toward the north in the 

 upper part of the series. The general succession and correlation 

 are as follow : 29 



