1862.] B1GSBY — CAMBEIAN AND HUEONIAN. 37 



II. Characters of the Cambrian. — The Cambrian formation is so 

 varied in its particulars, and so familiar as a whole, that a definition 

 of it need not be attempted. 



We find in it, however, the following characters : — 



§ 1. In Northern and "Western Europe alone (or nearly alone) it 

 consists principally of purple and black clay-slates, often chloritic 

 and micaceous, together with conglomerates, grits, and sandstones, 

 placed almost indifferently on any horizon. 



§ 2. This schistose constitution is elsewhere absent, except in one 

 or two localities ; and usually if any rocks exist intermediate between 

 the Silurian beds and a crystalline base, those rocks are derived 

 from the latter, and have no mineral or pakeontological connexion 

 with the Silurian series. 



§ 3. Immediate contact (transgressive) between the Silurian and 

 the metamorphic rocks may be said to be more general and more 

 extensive than between either the schistose or the simply conglome- 

 ratic rocks above mentioned, which are themselves, perhaps, about 

 equal in extent. 



§ 4. The Cambrian has a tendency to assume a local character, 

 inclining perhaps to the mixed schistose character mentioned in § 1, 

 the typical form as heretofore considered. 



§ 5. The various beds, argillaceous, arenaceous, &c, are incon- 

 stant in their succession, i. e. they have different horizons ; and some 

 may be absent altogether. 



§ 6. They vary also in their thickness, both as a whole and in 

 the individual beds. 



§ 7. Some of the mineral substances essential to organic struc- 

 ture, such as lime, phosphorus, fluor, azote (?), are absent, except a 

 little of the first, and that rarely. 



§ 8. With a large and varied assemblage of highly organized life 

 in the lowest Silurian deposit, we find this older, but kindred set of 

 rocks to be almost totally wanting in evidences of animal and vege- 

 table existence. Such forms as do appear are of low organization, and 

 do not indicate a fauna differing essentially from that of the Silurian 

 scheme : life is not here another, and an original, conception. 



§ 9. The Cambrian is not the Huronian. 



a. Typical Form and Distribution. — The description given in § 1 

 may be taken as representing very briefly the typical form of the 

 Cambrian as generally understood, and as first seen in Wales by 

 Professor Sedgwick. It has since been traced, with modifications, 

 into Ireland, Brittany, De'p. Loire Infcrieure, &c, in France, as well 

 as into Thuringia and Bohemia, and less distinctly in a few other 

 districts. 



Many of the leading facts in Cambrian geology may be learnt by 

 consulting the large Table at the end of this part of the paper ; and 

 still more satisfactorily by recourse to the original authorities, as 

 set down in the footnote*. 



* The principal authorities on the Cambrian Formation are as follows : — • 

 England and Wales. — Professor Sedgwick. Proc. Greol. Soc. and Quart. Journ. 



