~~ 
Introduction to Geology. 67 
of some disturbing force which was not extended into the 
upper series. The products of the lower section are by far 
the most valuable in the entire system of rocks. 
There appears considerable difficulty in admitting the sepa- 
ration of the transition and secondary orders at the point 
assigned by some writers ; that is, between the mountain lime- 
stone and the coal measures. The former conforms so com- 
pletely to the disposition of the beds of the latter, that it really 
seems impossible to view them but as parts of one great class. 
Neither is the argument founded on the “ truly remarkable 
difference in the nature of the organic remains,” in the coal and 
limestone formations, wholly free from objection ; because the 
genus Prodicta is common to the mountain limestone, the 
shale, and the argillaceous iron ore between the coal seams, in 
frequent cases, particularly in the great South Wales basin. 
The parallelism, inclination, and curvature of the beds of 
old red sandstone, are so conformable, also, to those of most 
coal fields, that it seems equally difficult to separate them there. 
(See figs. 107. 114. and 117. Vol. I.) On the other hand, it is 
urged that the mountain limestone is allied to, if not identical 
with, the acknowledged transition limestone, and that the ‘ old 
red sandstone possesses all the mineral characters of greywacke 
except the colour;” and Mr. Coneybeare admits that, in 
many instances, “ the limits between this series and that of 
transition rocks, can only be arbitrarily assigned ;” and fur- 
ther, that ‘* at least ten characters wi'l be found in common 
between them, for one which would lead to an opposite ar- 
rangement.” 
So many circumstances, geographical as well as geological, 
concur to associate these formations, that it appears desirable 
so to treat them; and it then remains to be determined whe- 
ther such associated formations should be transferred to the 
transition class, or remain the lowest section of the secondary. 
In the unsettled state of the controversy, we incline to the 
latter ; and conceive that we should more effectually extricate 
ourselves from theory, by adopting the alternative offered in 
Mr. Coneybeare’s arrangement, under the characteristic appel- 
lation of the carboniferous order. 
Hartside Fell, 
—~ 
Mountain Limestone, 
Whinsill Trap, = 
Limestone [ SS 
Old Red Sandstone, 
S35" 
Vertical beds of Coal, 
Grit, and Limestone. 
Trap, or 
Greywacke Sluted 
Sandstone, ~ Wihinsill . 
