188 STRATIGRAPHICAL GEOLOGY 



Series of North Wales and Westmoreland was derived (see Building 

 of the British Isles, 3rd edition). 



The much greater thickness of Silurian deposits in Norway and 

 Scania (as compared with the underlying Ordovician) also testifies 

 to the nearer presence of land. There was, however, the same 

 open sea over the Baltic area wherein little but limestone was 

 deposited. In the North British area, too, the same strip of 

 comparatively deep water persisted for a time with small 

 sedimentation, though after the epoch of the Birkhill shales the 

 whole British area received a large share of the detritus carried off 

 the land which lay to the north and north-east of it. 



The Silurian Sea probably extended over the same parts of the 

 European region as were covered by that of the Ordovician period, 

 but the land of Ardennes and the Rhine provinces, which may 

 have existed in Ordovician time, becomes much more of a certainty 

 in Silurian time. Thus in Belgium the Silurian extends south- 

 ward to the Crete du Condroz, which separates the basins of Namur 

 and Dinant, but must be overlapped farther south by the Devonian, 

 for it does not emerge on the Cambrian areas of Rocroi and 

 Stavelot (see Fig. 70, p. 216). Passing eastward we find the 

 Devonian rocks forming a continuous band through the Eifel, 

 Hunsruch, and Taunus districts, and resting near Frankfort on 

 Cambrian exactly as they do in the Ardennes. 



Southward the land probably included the Odenwald and the 

 Schwarz Wald of Baden, together with the Vosges district on the 

 western side of the Rhine, where a patch of Devonian lies directly 

 on the crystalline Archaean rocks, and no Silurian or Ordovician 

 occur. It may have extended still farther south into Switzerland, 

 but of this there is no actual evidence. The region above indicated 

 measures about 230 miles each way, i.e. from west to east and 

 from north to south, so that it probably included an area of over 

 70,000 square miles, which is nearly as large as England. 



Silurian strata are not found again till we go as far east as the 

 Carnic and Carinthian Alps in Austria, and as far south as 

 Sardinia, but this is probably due to their concealment by newer 

 rocks, and it is very likely that the Silurian Sea was continuous 

 from the south of France (Pyrenees and Languedoc) through 

 Northern Italy to Carinthia, Styria, and Bohemia. 



It is noticeable that in Southern Europe, i.e. in Languedoc, 

 Pyrenees, Spain, the Carinthian Alps, and Bohemia, the fauna found 

 in the Silurian strata is very different from that in the more 

 northern areas ; so that two distinct life provinces seem to have 

 existed at tcis time in the European region. 



The conditions of deposition which prevailed in this Silurian 



