TERTICAL, INCLINED, AND lORlZONTAL STRATA. 239 



the bed D, ihence it will again be uniform, though perhaps different from 

 the former, till we reach the stratum C, when again it will prove uni- 

 form over a considerable space till we begin to climb the bill to B. So 

 the whole hill-side in ascending to B will be of one and the same kind 

 of soil. But as we descend on the other side and pass B, we get upon 

 the edges of the beds, and then as we proceed from one bed to another, 

 the quality of the soil may vary every few yards, more or less, ac- 

 cording as the members of this group of heds are more or less differ- 

 ent from each other. But when we ascend the hill to A, where the 

 beds, besides being vertical, are also very thin, the soil may change at 

 almost every step, provided — which is, however, rarely the case among 

 the rocks (slate rocks) which occur most frequently in this position — pro- 

 ►vided the mineralogical characters of the several vertical layers be sen- 

 sibly unlike. Such dissimilarities in the angular position of the strata, 

 as are represented in the. above diagram, are of constant occurrence, not 

 only in our islands, but in all parts of the globe ; and they illustrate very 

 clearly one important natural cause of that want of uniformity in the na 

 ture and capabilities of the soil which is more or less observable in ever^ 

 undulating and in some comparatively level countries also. 



It may be stated, as the general result of an extended examination 

 of all the stratified rocks yet known — that they consist of alternations or 

 admixtures of three kinds of rock only — of sand-stones, of lime-stones, 

 and of clays. The sand-stones are of various degrees of solidity and 

 hardness, from the loose sand of some parts of the lower new-red and 

 green-sand formations, to the almost perfect quartz rock not unfrequently 

 associated with the oldest strata. The lime-stones vary in like manner 

 from the soft chalk to the hard mountain lime-stone and the crystalline 

 statuary marble ; while the clays are found of all degrees of hardness 

 from that of the London and Kimmeridge clays, which soften in water, 

 to that of the roofing slates of Cumberland and Wales, — and even to 

 that of the gneiss rocks which rest immediately upon the granite, and 

 which appear to be only the oldest cla3's altered by the action of heat. 



But the stratified rocks, though thus distinguishable into three main 

 varieties — rarely consist of any one of these substances in an unmixed 

 state. The sand-stones not unfrequently contain a little clay or lime, 

 while the lime-stones and clays are often mixed with sand and whh 

 each other. 



If the stratified rocks thus consist essentially of these three substances, 

 the soils formed from them by natural crumbling or decay must have a 

 similar composition. A sandy soil will be formed from a sand-stone,— 

 a calcareous soil from a lime-stone, — a clay from a slate or shale, — and 

 from a mixed rock, a soil containing a mixture of two or more of these 

 earthy ingredients — in proportions which will depend upon the relative 

 quantities of each which are contained in the rock from which they have 

 been derived. 



§ 7. Relative positions and peculiar characters of the several strata. 



1°. The several strata, or series of strata, which present themselves 

 in the crust of the globe, always maintain the same relative positions. 

 Thus the numbers 3, 2, 1, in the annexed diagram, represent three series 

 of beds known by the names of the magnesian lime-stone, the lower new- 



