192 
THE GEOLOGIST. 
Porous. Non-Porous. 
Inferior oolite 
Sand 
Upper lias shale 
Marlstone 
Middle lias shale 
Lias limestone 
Lower lias shale 
Variegated marls 
{Variegated sandstones & 
conglomerate 
Knottingley limestone 
Gypseous marl 
Magnesian limestone 
Marl slate 
R,o thetodteliegende 
From the Carboniferous system downwards m the 
series^ generally porous ; the alternations are^ firstly^ 
coal and sandstone ; then^ sandstone and limestone — 
limestone and slates — slates and granite^ or primary 
rocks. 
We shall^ in a future portion of our essay, make use of 
this comparative table, and we will not therefore test its 
adaptation in nature to the process of drainage, until the fact 
speaks for itself : by this means we shall avoid recapitulation 
and unnecessary length. 
The inquiry resolves itself, by what we have shown in the 
preceding remarks, into a very simple comparison — 
The rise and fall of ground The elevation of primitive and 
transition rocks 
The collection and distribu- The comparison of porous and 
tion of surface waters non-porous rocks in their 
reciprocal relations. 
