92 



LITHOLOGICAL GEOLOGY. 



may be produced by the slope of the sea-bottom in certain cases ; and, 

 off the mouths of rivers, in lakes (Fig. 95), quite a considerable incli- 

 nation may result from the fact that the successive layers derived 

 from the inflowing waters have taken the slope of the bottom on 

 which they fell. The sand deposits made over the slope of a sea- 

 beach between low and high tide are another example ; they take the 

 slope of the beach, as stated on page 82. Cases of inclined position 

 from this cause are necessarily of limited extent, ssince the conditions 

 required are not likely to exist on a large scale. 



It follows from these facts, that, unless strata have been disturbed 

 from their natural positions, the order in which they lie is the order of 

 relative age, — the most recent being highest in the series. 



(2) Dislocations of strata. — Strata, although generally in hori- 

 zontal positions when formed, are often, at the present time, tilted, or 

 inclined, and the inclinations vary from a small angle to verticality, 

 or even beyond verticality. They have been raised into folds, each 

 fold often many miles in sweep and equal to a mountain-ridge in 

 extent. They have been crumpled up into groups of irregular flex- 

 ures, one fold or flexure succeeding to another, till like a series of 

 wrinkles — and necessarily coarse wrinkles — on the earth's surface. 

 Every mountain-region presents examples of these flexures ; and most 

 intermediate plains have at least some undulations in conformity with 

 the system in the mountains. 



In connection with all this uplifting, there have been fractures on a 

 grand scale ; and strata thus broken have been displaced or dislocated 

 by a sliding of one side of such a fracture on the other, through vary- 

 ing distances from a few feet to miles, — one side dropped down to this 

 extent, or the other side shoved up. 



The subject of the dislocations of strata is hence an important one 

 in Geology. 



Uplifts, Folds, Dislocations. — The following sections illustrate the 

 general facts respecting these uplifts, dislocations, and folds. 



Fig. 96. Fig. 97. Fig. 97 A. 



Fig. 96 represents a part of the Coal-formation, dislocated along the 

 lines of fracture a a and b b, the beds (the coal-beds 1 and 2 and the 

 other layers) being displaced as well as disjoined in the fracturing. 



