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BRITISH FOSSILS, STRATIGEAPHICALLY AEEANGED. 



Br John Moeeis, P.G.S. 



I. PALEOZOIC SYSTEM. 



The Palaeozoic System comprises the earliest fossil-bearing strata. 

 These have collectively a great thickness, and are of various mineral 

 characters; being argillaceous, arenaceous, and calcareous, generally 

 indurated, and occasionally metamorphosed. 



As a general rule, these strata appear in the western and north- 

 western districts of Britain, and, to a considerable extent, in the mari- 

 time districts of Ireland. The rocks of this system contain the chief 

 metaliferous workings, as in Cornwall, IS'orth Wales, Cumberland, 

 Scotland, &;c. The upper portion, namely, the Carboniferous, affords 

 the chief source of our lead-ores which occur in the limestone of 

 Derbyshire, Tlintshire, and Cumberland ; and the associated shales and 

 sandstones, forming the Coal-Measures, contain the well-known ex- 

 tensive deposits of fossil fuel and iron-ore. 



The palaeozoic strata are numerous enough and sufiSciently distinct 

 among themselves to form several series. The first or lower of these 

 comprises the Cambrian and Silurian; the middle is the Devonian; 

 and the uppermost includes the Carboniferous and Permian. 



1. Lower Paleozoic Rocks. 



(Cambrian and Silurian.) 



The lower portion of the palaeozoic system has two great groups of 

 rocks; the lower one is named Cambrian by the Rev. Professor 

 Sedgwick,— from its great extent in Wales ;— the other is called 

 Silurian by Sir Roderick Murchison, on account of the typical strata of 

 this p;roup having been worked out by him in the country once in- 

 habited by the Silures,— the border-counties of England and Wales, 

 where the group is extensively developed. 



