THE ORDOVICIAN PERIOD. 341 



them, and where erosion has cut off the beds which once overlay them. 

 Ordovician beds are not certainly known in the northern Alps, though, 

 the system may be represented by metamorphic rocks. It is present 

 in the southern Alps. In France the system carries a bed of iron ore 

 rarely more than six feet thick, which is commercially valuable. In 

 its character and occurrence, it recalls the Clinton ores of the United 

 States. 1 



In Bohemia, though the system does not appear at the surface 

 over a great area, it has been made classic by the paleontological work 

 of Barrande. 2 The formation is here rich in fossils, and the faunas 

 of few areas in any part of the earth have been studied with equal 

 care, or with richer results. In contrast with the great abundance 

 of fossils in Bohemia is their paucity in the corresponding formations 

 of Germany. 



Barring somewhat extensive volcanic action, the Cambrian and 

 Ordovician periods were periods of general quiet in Europe, as in 

 America; but at the close of the Ordovician considerable disturbances 

 resulting in geographic changes of importance took place. Stated 

 in other terms, it was these disturbances which brought the Ordo- 

 vician to a close. These general conclusions are based on the fact 

 that the Ordovician system of Europe is generally conformable on 

 the Cambrian, while over considerable areas it is unconformable beneath 

 the Silurian. This is especially true in the British Isles, where pro- 

 found dynamic changes intervened. Here the stratigraphic relations 

 of the systems show that at the close of the Ordovician, the strata 

 which had been but recently laid down beneath the ocean were ele- 

 vated, folded, crumpled, and so metamorphosed as to greatly change 

 their character. In the Highlands of northwestern Scotland the 

 dynamic action seems to have been exceptionally severe. Here the 

 strata were not only folded, but the folds were overturned, and a series 

 of nearly horizontal faults or thrust planes developed. Locally, the 

 thrust was as much as ten miles, 3 and had for a result the burial of 

 the Ordovician strata, sometimes without metamorphism, by the 

 Cambrian and even the Archean rocks. Over the greater part of the 



1 DeLapparent, Traite de Geologie, 3d ed., p. 800. 



2 Systeme Siluriene de la Boheme. 



3 Quart. Jour. Geol. Soc, 1884 and 1888. The latter article gives references to 

 preceding literature on this interesting area. 



