36 
DESCRIPTION OF THE ROCKS 
there is but one series of periodically and locally variable mineral 
terms, but one vast successon of organic forms — suited to the suc- 
cessive conditions of the sea, the land, and the air. 
NORTHERN TYPE. 
Upper Limestone Series. 
The most general character of the lower limestone series is sim- 
plicity, but of this upper series, complexity. As in the case of 
the lower scar limestone, the complexity of the formation augments 
toward the north. The southern series (Craven) consists almost en- 
tirely of argillaceous laminated rocks, locally changing to limestone and 
chert, generally productive of ironstone, and containing marine ex- 
uvige ; the northern type (Teesdale) consists of the same argillaceous 
basis, (less calcareous and of a coarser grain), with the addition of 
many layers of sandstone, distinct beds of limestone, thin coal seams, 
and land plants. In the intermediate districts the coal vanishes, the 
limestones are reduced to a small thickness, the sandstones become 
interlaminated with the shales, and the observer feels himself to be 
in possession of the key of the system of variation. 
On the one side, (the northern and western), are the variable effects 
of inundations from the land, and the inconstant movements near 
the shores of the sea ; on the other, more continual and uni- 
form depositions beneath deeper and more tranquil waters. On this 
distinction of littoral and oceanic deposits, which is found with the 
same geographical relations in the oolitic series of the North of Eng- 
land, (see the first Volume of this Work, and Encyelop. Metrop. 
Article, Geology), appears to me to depend the solution of many of 
the problems of difference between contemporaneous deposits, which 
are beginning to occupy the attention of geologists. It is by this 
mode of surveying that we may hope to arrive at a knowledge of 
the ancient Hydrography of the globe. 
We shall choose, as a general standard of reference for this com- 
plex series of rocks, that district where this character of complexity 
