403 
[Foerstej 
broke down and their subterranean valleys became exposed to the 
open air. 
8a. Consideration of the preceding Theories. Faults. — If the 
cross valleys here considered be due to faults, the presence of the 
latter has escaped me. The accordance between the strata ex- 
posed on opposite sides of the cirques , their strike and dip at cor- 
responding points in the fold, is too great to make faults at all 
likely. Even where there seems to be a little discordance it 
is necessary to be very careful, since the strike and dip of any 
layer at its exposure in the cirque are not necessarily the strike 
and dip for this layer as far as the center of the cirque. An ex- 
amination of the strikes and dips of the rocks at various parts of 
the folds shows that the folds are by no means so regular as one 
might suppose, but that, although perhaps these Jura folds are the 
most regular of any known folds of the same magnitude, many 
changes of strike and dip occur all over the surface of the folds, 
changes which attract little attention where the fold is known to 
be continuous, but which are given undue weight when found on 
either side of the cirques , with their supposed faults. Moreover, 
the more rapid erosion of the shales has at times given new dips 
and strikes to the remaining strata, at their terminations in the 
cirques. It is evident that the farther the corresponding strata 
are removed on opposite sides of the folds, the greater must be the 
chance for error. I have therefore paid particular attention to 
searching for faults where the strata on opposite sides of the 
cirques approach within a very few feet of each other, but their 
presence has escaped me. On the contrary, the evidence that the 
strata on opposite sides of the cirques are in accord seemed suffi- 
ciently accumulative to warrant the general denial of faulting here. 
These observations seem so important that the best localities for 
exemplifying them are here noted, together with other facts of less 
relevant nature. 
8b. Special Account of various Cirques. — (See PI. X.) — The 
Boujean cirque is more properly a cluse or gorge, with steep sides 
up to a level of 640 meters above sea. The lower part of the gorge 
has precipitous walls, and it is very evident that the stream has 
been rapidly deepening its channel here, and that hence no great 
age can be assigned to most of the existing valley. Owing to the 
precipitous walls, beautiful sections are exposed to view in close 
proximity across the gorge, and still there is no evidence of fault- 
