THE CAMBRIAN PERIOD. 



79 



The opposite may be regarded as giving a typical series of 

 the Cambrian Rocks in a typical locality; but strata of Cambrian 

 age are known in many other regions, of which it is only 

 possible here to allude to a few of the most important. In 

 Scandinavia occurs a well-developed series of Cambrian de- 

 posits, representing both the lower and upper parts of the 

 formation. In Bohemia, the Upper Cambrian, in particular, 

 is largely developed, and constitutes the so-called " Primordial 

 zone " of Barrande. Lastly, in North America, whilst the Lower 

 Cambrian is only imperfectly developed, or is represented by 

 the Huronian, the Upper Cambrian formation has a wide ex- 

 tension, containing fossils similar in character to the analogous 

 strata in Europe, and known as the " Potsdam Sandstone. " 

 The subjoined table shows the chief areas where Cambrian 

 Rocks are developed, and their general equivalency : 



TABULAR VIEW OF THE CAMBRIAN FORMATION. 



Like all the older Palaeozoic deposits, the Cambrian Rocks, 

 though by no means necessarily what would be called actually 

 " metamorphic, " have been highly cleaved, and otherwise altered 

 from their original condition. Owing partly to their indurated 

 state, and partly to their great antiquity, they are usually found 

 in the heart of mountainous districts, which have undergone 

 great disturbance, and have been subjected to an enormous 

 amount of denudation. In some cases, as in the Longmynd 

 Hills in Shropshire, they form low rounded elevations, largely 

 covered by pasture, and with few or no elements of sublimity. 

 In other cases, however, they rise into bold and rugged 



