482 GEOTECTONIC (STRUCTURAL) GEOLOGY. [Boox IV. : 4 
and new layers (d) may be laid down conformably over the whole. 
Among the lessons to be learnt from such sections of local irregularity, 
one of the most useful is the reminder, that the inclination of strata 

ad 




Fic. 194.—Contremporanrous Erosion and Deposit (B.). 
may not always be due to subterranean movement. In Fig. 195, for 
example, the lower strata of shale and sandstone are nearly horizontal. 
The upper thick sandstone (b') has been cut away towards the left, 
and a series of shales (a’) and a coal-seam (c') have been deposited 
against and over it. If the sandstone was then level, the shales 
must have been laid down at a considerable angle, or if these were 
deposited in horizontal sheets, the earlier sandstone must have 
accumulated on a marked slope. As deposition continued, the in- 


Fic, 195.—ConrEemporanrovus Erosion wira Inctinep AND HorizonTaL Deposirs, 
iN CoaL Measures, Ketto Water, SANQUHAR, DUMFRIESSHIRE. 
a’, shales and ironstones; b, b’, sandstones ; ¢, ec’, coal-seams. 
clined plane of sedimentation would gradually become horizontal 
until the strata became once more parallel with the series a b ¢ 
below. A structure of this kind, not unfrequent in the Coal-mea- 
sures, must be looked upon as a larger kind of false-bedding, where, 
however, terrestrial movement may sometimes have taken place, 
In the instances here cited, it is evident that the erosion took 
place, in a general sense, during the same period with the aceu- 
mulation of the strata. For after the interruption was covered 

