Conylomerates, and Marls of Devonshire. 
43 
But to proceed to the second objection. Faults arc un- 
doubtedly numerous throughout the district ; but almost all of 
them are of very limited extent. Moreover, the effect of a fault 
may be either to enhance or to depreciate the apparent thickness 
of a series of strata ; the required correction is not necessarily 
subtractive. If the beds are let down in the direction towards 
which they dip, the apparent thickness will be less than the real ; 
but if they are raised in this direction, the effect is reversed. Let 
figure 3 represent a cliff section composed of a series of inclined 
beds which have been so faulted at C that the strata on the right 
or dip side of the fault are lower than on the opposite side ; and, for 
the sake of simplicity, let it be supposed that the fault is vertical 
and that it has made no change in the amount or direction of the 
dip. It is obvious that since the beds 5, 6, 7 do not occur at the 
base of the section, the measured horizontal extension, and there- 
fore also the calculated thickness of the formation, will be less 
than the truth. Next, let the Section represented in Fig. 4 differ 
from the preceding only in having the beds raised on the dip side 
of the fault ; here it is seen that the beds 1, 2, 3, 4 occur twice at 
the base ; hence the measured length of the section and its calcu- 
lated thickness will be greater than the truth. In general terms, 
therefore, the calculated thickness of a series of faulted strata will 
be greater or less than the real thickness, according as the beds are 
higher or lower on the dip side of the fault, than they are on the 
opposite side. 
We have now therefore two questions before us: 1st. What 
is the character of the faults which are known to exist in the red 
rocks of south-eastern Devonshire ? 2nd. Is it probable that the 
formation contains important undetected faults such as would 
cause its calculated thickness to be much above the truth ? 
So far as I have observed, the faults in Torbay, as well as 
between the Straight Point and Ladrum bay, raise the beds on the 
dip side ; on the other hand, those between Dawlish and the Exe, 
and between Sid mouth and Culverholc Point lower them. From 
