844 



PRINCIPLES OF STRATIGRAPHY 



intervening synclines. The resultant outcrops have l)een discussed 

 in the preceding chapter. 



When anticHnes are partly eroded a series of monoclines or 

 hog-backs results, similar in character to that formed by the uplifted 

 upper end of the coastal plain as above described. JMonoclines 

 formed by breached anticlines usually occur in pairs opposing each 

 other as in the Appalachians of to-day, but monoclines without a 

 corresponding opposite occur which in reality represent one limb 

 of an anticline of which the other limb has been entirely removed. 

 (Fig. 216.) Thus the monocline which forms the Front Range 

 of the Appalachians in New Jersey, Pennsylvania and southward 



rKvjJothelical'iFalao^oicif'ection aaoss the QKotValhij at Xarrtslurj. 

 ifo il last, ate Chap XXII offfmaJ ^eporf, 1^91 



g placed aloHij lines AB,CD. 



mThTman. 



HI, CoatMeojurcs 



til Jotlsnllc Cmgbmemte 



u MaacfiOiuntrtdshaU ' 



' ii^pip :^ciii<is/one 



It CaMill. 



miOicmunq JtarccUiu <Sc 



I Clinton, Sc 

 IV Medina &c 

 HI Great yalley slates 



II Crcat raUeulimeitone . 

 'MrsnoUJ Trias) york. 



7/iu ieeTioa /Jwwl merely tfu orent deptit cfihe 



Cotv Suilclinal^ but not Us cxurt ahape uiidtr 



ground. St indicates the dose plications also of the 



yilate anil limestone iclts; and thi rast Jlermt Erosion 



Fig. 216. Section of the Appalachian folds near Harrisburg, to show the 

 removal of the eastern part of the folds by erosion. 



represents merely the western limb of an anticline, the eastward 

 continuation of which has been entirely removed by erosion. This 

 was accomplished by peneplanation which cut below the axes of the 

 synclines into the underlying more intensely folded rocks in which 

 the Appalachian folds are not recognizable. The same is in part 

 true of the monoclines facing the Front Range of the Rocky Moun- 

 tains. The Triassic and Cretacic strata most probably once ex- 

 tended across what is now the front range axis, and this was per- 

 haps true of much of the Palaeozoic series as well. From the fact 

 that the axis of the long Front Range anticline was a granite one, 

 erosion, which removed the formerly continuous sediments, left it 

 in relief, so that it holds the same relation to the flanking mono- 

 clines on either side that the central crystalline mass of the Black 

 Hills holds to its encircling hog-backs. ( Fig. 213, c. d, p. 840.) The 

 completion of the cycle of erosion in a region of monoclinal flexures 



