50 W. Pengelly on the Red Sandstones, dc. 
fragmentary beds which remain. It may be observed also that, for 
anything which appears to the contrary, the intercalated period of 
unbuilding may have been immediately preceded and succeeded by 
intervals of quiescence, intervals which in each case separated 
those of the reversed activities. 
Facts connected with diagonal stratification, so frequently and 
so beautifully displayed in the sandstones and finer conglomerates, 
teach the same truth. * They, like those just dismissed, are in- 
deed inexplicable except on the hypothesis that the period repre- 
sented by our Red rocks was one, not of uninterrupted sedimenta- 
tion, but in which the processes of rearing were frequently inter- 
mitted and occasionally exchanged for those of razing. Its duration 
is not measured by the volume of the rocks deposited within it, 
nor by the time necessary for the pre-requisite denudation ; if we 
even estimate at its full value the minute trituration which in very 
many cases the materials have undergone, we still fall short of the 
truth, for each and all of these omit the large item of re-denudation, 
which was again and again repeated. 
I have purposely abstained from introducing the question of 
the prevalent jointage of the Trias ; the subject is too large to be 
discussed in the present paper ; and its relations and ramifications 
are so numerous and so various, as to suggest that it should be un- 
dertaken by some one prepared to produce a general monograph on 
" The Divisional planes of the Rocks of Devonshire and Corn- 
wall." 
In conclusion, I beg to thank you Mr. President, and, through 
you, the Council of the Institution, for having allowed me a third 
time to bring the Red Rocks of our county under discussion ; and 
I desire also to express my appreciation of the kind way in which 
my papers have been received by the members who have done me 
the honor to be present. 
* See " Transactions of the Devonshire Association for the Advancement 
of Science, Literature, and Art," 1863, page 37, &c. 
