6S 
REPORT— 1847* 
The folds will then be such as indicated by the continuous lines. One 
side of each fold is here much longer than the other. 
Again, it is immediately seen by inspecting the figs. 4, 5, that the com* 
pressing horizontal forces acting on the central and subsiding masses PS and 
P'S' must distort each mass from its original form, in such a manner that if 
the vertical sections of those ma-sses when undisturbed were rectangular, the 
angles at P aud S, and at P' and S' would become acute, and the other 
angles obtuse, by the distortion produced by compression. The compres¬ 
sion of the rectangular mass PMSN (fig. 8) has been supposed such if 
would not destroy its rectaiigularily; but if the compressing force acted on 
it as on the mass defined by the same letters in fig. 5, it would manifetly 
be deformed into the oblique-angled parallelogram indicated by the oblique 
angles at M and N (fig. 9), and the folds would assume the form there 
Fig. 9. 
represented, the axis of each fold being inclined to the vertical, aud dippi**c 
in the same direction as the uncompressed beds. 
The flexures which have been directly contemplated in the above expla¬ 
nation are those on a scale comparatively small, but the same explanation 
would be applicable to those on any larger scale. The mechanical cans® 
of the phenomena, according to this view of the subject, is horizontal pres- 
sure; the unsynimetrical character of the folds in fie. 8 is attributable to 
the oblique position of the beds with reference to the horizoutal direction 
of the compressing force; and the iuclinatioti of the axes of the folds^ 
represented in fig. 9, is due to that action of the comprcs.«ing forces by 
which the form of the whole mass containing the folded strata has 
twisted and distorted from its original form, as above described. Tht® 
oblique character of flexures on a Urge scale, has been particularly observed 
lachian^SaU interesting description of the Apa- 
28. InverM Slrala.~U the flo.xercs above represented (Sg. 9) I* » 
• Coiitrihulions to ihe Geology of the United States. 
