520 GEOLOGY 



over a great area, it has been made classic by Barrande, 1 who has 

 studied its abundant fossils in great detail. The faunas of few 

 areas in any part of the earth have been studied with equal care, or 

 with richer results. 



The Ordovician of Europe is generally conformable on the 

 Cambrian, but over considerable areas it is unconformable beneath 

 the Silurian. In the British Isles, the stratigraphic relations of 

 these systems show that the Ordovician strata were elevated, 

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

 character at the close of the Ordovician period. In the highlands 

 of northwestern Scotland, the dynamic action seems to have been 

 exceptionably severe. The strata here 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, 2 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 European continent, 

 on the other hand, orogenic disturbances do not appear to have 

 taken place at the close of the Ordovician. In Europe, as in 

 America, the great disturbances took place where thick bodies of 

 sediment had been accumulated (or else the beds were greatly 

 thickened by the disturbances). 



In other continents the Ordovician strata have not always been 

 separated from the overlying Silurian, but they are known both in 

 Australia and China. 



Duration and Climate 



The duration of the Ordovician is perhaps no better known than 

 that of the Cambrian, but the period was probably somewhat 

 shorter than its predecessor. 



Neither in Europe nor in America is there decisive evidence that 

 climatic zones were distinctly marked. All that is known of the 

 life of this area would seem to indicate that the climate was much 

 more uniform than now throughout the areas where the strata of 

 the period are known. The fact that the Ordovician rocks have 



1 Syst&me Siluriene de la Bohdme. 



2 Quart. Jour. Geol. Soc., 1884 and 1888. 



