HYPOGEIC WORK. 369 



folded dotted layers below are quartzytes, and the beds below, shales. 

 (La Fouche, India Survey, 1888.) 



3. Arctic upturned rocks. — Flexures as a result of lateral pressure occur 

 in the Arctic regions. On Grinnell Land, from Scoresby Bay to Cape Cress- 

 well, in lat. 82° 40' K., slates, limestone, grits, and quartzytes are in sharp 

 folds, and often vertical, with the strike E.jST.E. — Feilden & De Eance on 

 the results of the Sir George Nares Expedition in 1875-76. 



For other examples of orogenic movements see pages 534, 808-812, under 

 Historical Geology. 



CoNCLusiOK. — Orographic work has been carried forward, in general, by 

 means of flexures, fractures, and slips or faultings along fractures ; and the 

 faults have largely been flexure-faults, — that is, have been made in connec- 

 tion with the production of more or less pronounced flexures. 



Subordinate Effects attending Orographic Movements. 



Among subordinate orographic effects are Ji7'st, those incidental to the 

 friction, and the heat thereby produced, namely : (1) part of metamorpliism, 

 (2) of vein-maJcing, and (3) of volcanic phenomena — subjects already con- 

 sidered. 



Second, those incidental to the pressure : these are (4) variations in the 

 characters of flexures ; (5) distortions of beds and of fossils ; (6) slaty 

 cleavage or foliation; (7) joints. 



Third, (8) earthquakes. 



1. Effects Incidental to the Pressure. 



1. Variations in flexures. — The characteristics of flexures have already 

 been illustrated and explained (page 101). The pressure producing them 

 -encounters unequal resistance from inequality of mass in the pile of strata 

 along the axis of the area of disturbance ; from unequal consolidation, or 

 fe-mness, or rigidity, in the beds ; and also from friction against the floor of 

 rock beneath. For these reasons flexures of the ordinary kind always have 

 the ridge-line inclined, and are irregularly distributed along an area of 

 disturbance. 



The Wasatch Mountains (Fig. 335) illustrate the influence, on the flexures, 

 of the floor of rock underneath the moving strata, and show that a flexure 

 may be made with its axis in the line of the pressure and be thrust forward 

 end foremost. 



The minor flexing or wrinkling of beds, not uncommon in the fine slaty 

 rocks and schists, is often occasioned by unequal yielding to pressure in 

 the beds, unequal rigidity, unequal contraction ; and it may also come from 

 feeble oscillations in the action of the moving force, and from the action of 

 gravity on the highly upturned or vertical beds. 



2. Distortions of beds and their fossils. — The beds subjected to the 

 •enormous pressure were more or less yielding. Argillaceous strata are soft 



DANA'S MANUAL — 24 



