184 
GENERAL VIEWS. 
From all this a conclusion arises that the calcareous members of the 
Yoredale series (except those of the fourth and fifth terms) have their 
maximum toward the east, the argillaceous beds toward the south 
and south-west, and the grit rocks toward the north and north-west- 
The southern argillaceous type is prolonged into Derbyshire, Stafford- 
shire, Cheshire, and Flintshire, and* reappears in great force in the North 
of Ireland: with a less thickness of shales, it is represented in South 
Wales, Somersetshire, and Belgium. The northern argillaceous type 
reaches the Tweed, and spreads round the northern border of the 
Cumbrian slates. 
The inconstant members of the terms of the Y oredale series are coal, 
ironstone, and chert. It is evident in considering the occurrence of 
these substances, in the Yoredale rocks, that ironstone is very much 
most abundant in the argillaceous beds, and in the southern districts ; 
but coal on the contrary is most plentiful in the northern tracts where 
gritstones are more predominant. Chert becomes less and less plentiful 
as we leave Craven, and proceed northwards ; in Swaledale and A rken- 
dale it is found in great quantity, but does not abound further north. 
Origin of the substances. — The agencies concerned in the deposition 
of the different substances composing the mountain limestone formation 
being assumed to be located in the directions of the maximum thickness 
of each respectively, we may proceed to investigate the nature of those 
agencies, by comparing in some detail the character of the several sub- 
stances produced by them. The first circumstance to be dwelt upon 
is the distribution of organic remains. 
Organic remains are found in all the terms of the mountain lime- 
stone formation, and in all the substances composing them, but very 
unequally. All the limestones contain marine reliquiae ; the plates 
generally contain marine exuviae also, locally in the greatest possible 
profusion, but seldom where they are sandy , or interstratified with thin 
gritstones. The plate under main limestone contains fossils at Bowes ; 
that under the underset limestone in Fountains fell ; that under the 
