Conglomerates, and Marls of Devonshire. 
37 
to films not thicker than writing paper, and may be compared to 
loose plaster or pellicles of whitewash on a wall. Even the films 
sometimes cover considerable areas, and may be described as being 
built up of a series of superposed rows or lines of sand a single 
gi-ain in thickness, each row representing, and having been detached 
from, a distinct and separate lamina of sedimentation. The plates, 
whether thick or thin, are parallel to the clifi", and, therefore, at 
least, sensibly vertical. They are not coincident with, or parallel to, 
any recognizable divisional surface of the rock, whether of true or 
false stratification or of jointage, but are not unfrequently at right, 
and other high angles to them ; their appearance may be illustrated 
however by speaking of them as ha\ing been produced by Atmospheric 
agents which have detected and developed a latent cleavage in the 
rock ; or by supposing that of the forces which formerly .held the 
particles together, two only — those in the directions of the length 
and height of the plate — had been faithful to their trust ; the third 
— that in the direction of the thickness of the plate — having 
allowed them to be detached. On carefully removing a portion of 
one of the films it is found to divide along the lines of sedimenta- 
tion. It seems not improbable that the separation may have arisen 
from the atmospheric moisture, absorbed by the sandstone, pene- 
trating to a limited and uniform depth, where, by its gravity, or by 
changes of volume in consequence of changes of temperature, or 
both, it overcame the cohesive force which held the particles 
together. 
And now, though my notes are by no means exhausted, my time 
is more than gone. I cannot on this occasion enter on a 
consideration of the numerous facts which testify to the vast 
chronological value of the Triassic rocks of Devonshire, nor must 
I indulge in the pleasure of speaking of the Life History of the 
period which they represent. Though our Red rocks appear to be 
destitute of fossils, their era was by no means a lifeless one ; 
possibly it may have been less rich than some others in the amount 
and variety of its organic forms, though this idea must be 
understood rather as the exponent of our ignorance, than of our 
knowledge, of the Flora and Fauna of this, the earliest. Chapter of 
the Mesozoic volume of the Earth's history. We must not forget 
that rocks largely charged with peroxide of iron are usually very 
poor in fossils, nor that the St. Cassian beds, in the Austrian Alps, 
— believed to belong to the Trias — have somewhat recently yielded 
as many as 800 species of fossils. 
