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Show 184 EXPLORA'riON OF TflB OANONS OF TilE COTJORADO. above and the horizont.-1.l beds below, unbroken; the flexm·e is complete, and wo have a monoclinal fold, as represented in Figure 67. Still another variation is found. In the same vertical section we may sometimes see that a bed composed of a somewhat brittle material is broken so as to form a fault, while the bed above or below, composed of a more flexible material, is bent so as to form a fold, and thus a fault and fold will be represented in the same cross section as in Figure 68: rrhus it is seen that the transformation of a fold into a fault may occur in two ways-longitudinally alonO' the course of the fault, and vertically in the strata. b - rrhe flexures, or monoclinal folds, also change in character, for the dip of the beds may vary greatly-from two or three to ninety degrees-and if we trace such a fold along its course, commencing at its transformation fi·om a fault, we may find the flexure becoming less and less, until it can scarcely be detected. by the eye, and then, perhaps, increase gradually into an abrnpt fold, and then into a fault, reproducing, in some irregular way, the varieties of faulting above described. These faults run in lines approximately parallel, and divide the district under consideration into long belts, or blocks, and one edge of each block usually lies at the foot of an escal'pment, the other at the summit of an escarpment. In examining the down-throw of these blocks, it is observed that the edge which lies against the foot of an escarpment has usually been thrown down much more than the opposite one, so that the blocks are tilted more or less. The relative amount of the downfall of these two edges is ever· changeable. There are cases where the summit edO'e seems to have b preserved its original position without down-throw, and there are other cases where the summit edge seems to have fallen quite as much as the other. There is yet another change rung on these displacements. In some places the beds, at the edge of the table, lying against the foot of the escarpment, are turned down, while farther back from the fault, toward the summit edge, the beds are approximately horizontal. This is represented in Figure 70. Thus the long, narrow blocks, into which the country is divided by these displacements, are warped, or twisted. ~hese faults and folds, thus ever changing in their characteristics, produce hke changeable features in the topography of the country. A sharp ~ ,. u.t~"'o & • a .. • ~ . . ' oo: •."'::: ... •.• 0 ~ .. • • ft " ~ofJ "' •o: • : ... - ----- ' • _.... c c • ... f It Q .--.---------- ................. ...... ... ....... . h 1\s widely sopamtecl, tlle F . 66 -Section acr OHS a fanlt wtt wu k still ex.h·t b·l t·t og the tgore . . f\lled with broken roc ' intervemng space original stratification. :Figure 67 .-A lnonocliual fold. |