Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . Fig. 11.—Pitching Folds. (c) The overturned or recumbent fold (Fig. 12), inwhich actual inversion of the strata is to be observed inthe upper limb, as the result of forward movement dueto continued lateral pressure. In extreme cases recum-bent folds may be transformed into reversed faults andthrust planes. (d) Isoclinal folds arc those in which the two limbsare crushed close together in such a manner that the bedson the two flanks of a fold are parallel to each other, and THE STRU
Geological and topographical maps, their interpretation and use, a handbook for the geologist and civil engineer . Fig. 11.—Pitching Folds. (c) The overturned or recumbent fold (Fig. 12), inwhich actual inversion of the strata is to be observed inthe upper limb, as the result of forward movement dueto continued lateral pressure. In extreme cases recum-bent folds may be transformed into reversed faults andthrust planes. (d) Isoclinal folds arc those in which the two limbsare crushed close together in such a manner that the bedson the two flanks of a fold are parallel to each other, and THE STRUCTURE OF THE EARTHS CRUST 33 the appearance in section is as in Fig. 13, a and isoclines may be cither vertical or inclined. In casesof isoclinal folding, there is often much difficulty indetermining the true sequence of the strata, as beds arefrequently repeated at the surface, and unless they have. Fig. 12.— Recumbent Fold. very well-marked characters, it is in consequence almostimpossible to detect this repetition in the field. Types of fracture other than thrust planes are pro-duced by the action of gravity upon masses of the earthscrust detached from the surrounding blocks by shrinkage
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