THE CAMBRIAN PERIOD. 79 
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 repre- 
sented by the Huronian, the Upper Cambrian formation has 
a wide extension, containing fossils similar in character to the 
analogous strata in Europe, and known as the “ Potsdam Sand- 
stone.” The subjoined table shows the chief areas where Cam- 
brian Rocks are developed, and their general equivalency : 
TABULAR VIEW OF THE CAMBRIAN FORMATION. 
Britain. Lurofpe. America. 
a. Tremadoc Slates. | a. Primordialzone| a. Potsdam 
of Bohemia. Sandstone. 
6, Lingula Flags. 6, Paradoxides 6. Acadian 
Upper Schists, Olenus group of New 
Cambrian. Schists, and Dict- Brunswick. 
yonema schists of 
Sweden. 
a. Longmynd Beds. | a. Fucoidal Sand- Huronian 
stone of Sweden. Formation ? 
6. Llanberis Slates. | 0. Hophyton Sand- 
stone of Sweden. 
c. Harlech Grits. 
Lower ad. Oldhamia_ Slates 
Cambrian. of Ireland. 
e. Conglomerates and 
Sandstones of 
Sutherlandshire ? 
jf. Menevian Beds. | 
Like all the older Palzeozoic 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 eleva- 
tions, largely covered by pasture, and with few or no elements 
of sublimity. In other cases, however, they rise into bold and 
rugged mountains, girded by precipitous cliffs. Industrially, 
the Cambrian Rocks are of interest, if only for the reason that 
the celebrated Welsh slates of Llanberis are derived from 
highly-cleaved beds of this age. ‘Taken as a whole, the Cam- 
brian formation is essentially composed of arenaceous and 
