102 



LITHOLOGICAL GEOLOGY. 



1. The natural positions of strata as formed. — Strata in their 

 natural positions are commonly horizontal, or very nearly so. The 

 level plains of alluvium and the extensive delta and estuary flats 

 show the tendency in water to make its depositions in nearly hori- 

 zontal planes. The deposits formed over soundings along sea-coasts 

 are other results of sea-action ; and here the beds vary but little 

 from horizontality. Off the coast of New Jersey, for eighty miles 

 out to sea, the slope of the bottom averages only 1 foot in 700, — 

 which no eye could distinguish from a perfect level. As the processes 

 of the present period along coasts illustrate the grand method of 

 rock-accumulation in past time, it is plain that strata when in 

 their natural positions are very nearly, if not quite, horizontal. 

 Over a considerable part of New York and the States west and 

 southwest, and in many other regions of the globe, the strata are 

 actually nearly horizontal at the present time. In the Coal form- 

 ation, the strata of which have a thickness, as has been stated, of 

 five to fifteen thousand feet, there is direct proof that the beds were 

 horizontal when formed ; for in many of the layers there are fossil 

 trees or stumps standing in the position of growth, and sometimes 

 several of these rising from the same layer. 

 Fig. 94 represents these tilted coal-beds c, c, 

 with the stumps s, s, s. Since these trees 

 must have grown in a vertical position, or 

 at right angles to the ground, like all others, 

 and as now they are actually at right angles 

 to the layers, and parallel to one another, 

 they prove, whatever the present condition 

 of those layers, that originally they were horizontal. The posi- 

 tion of shell-accumulations and coral-reefs in modern seas shows, 

 further, that all limestone strata must have been very exactly hori- 

 zontal when they were in the process of formation. 



Fig. 95. 



Fig. 94. 



In sedimentary deposits, however, some variation from horizon- 

 tality 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 con- 

 siderable inclination may result from the fact that the successive 

 layers derived from the inflowing waters would take the slope of 

 the bottom on which they fall. Cases of inclined position from 



