the oldest rocks occupy that position. Where these dips 

 frequently in a short distance the deposits are said to be contorted. 

 Contortions of the Carboniferous rocks are well seen in the cliffs near 

 Clovelly in North Devon. 



The different rocks which compose the interior of the earth to a 

 considerable depth, therefore, in consequence of this inclination, crop 

 out, or are exhibited in succession on the surface ; and hence it is that 

 we are furnished with a vast variety of mineral productions which 

 otherwise would be deeply seated or hidden, and are able to predict 

 the nature of the beds which occur in succession beneath our feet. 



Continuity of Strata. Any one thus far initiated will be able 

 to construct a section or scale of the strata which occur in his own 

 neighbourhood, naming them in the exact order of their succession or 

 superposition, and thus will be furnished with the means of comparing 

 his own district with others near and distant. The results of this 

 comparison are very important, for we thus learn that one general 

 order of succession is observed among all the stratified rocks of Eng- 

 land. Certain strata are locally deficient, but all those which do 

 occur together are found invariably in the same relative position. The 

 series of stratified rocks in the North of England, taken in a general 

 way, is expressed by the following names: Chalk, Speeton Clay, 

 Kimmeridge Clay, Coralline Oolite and Calcareous Grit, Oxford Clay 

 and Kelloway rock, Cornbrash and Oolite rocks, Lias shales, Red 

 Marl and Sandstone, Magnesian Limestone, Coal series, Carboniferous 

 Limestone, and Slate. The series in the southern parts of England 

 is precisely accordant, except that the magnesian limestone is there 

 nearly deficient, that the Kimmeridge Clay is covered by some strata 

 which do not pass the river Humber, and the Speeton Clay is 

 replaced by the Neocomian Sands. Besides, we find the strata of the 

 north of England actually connected by mutual extension with those 

 of the same names in the south of England, so that we thus prove 

 their continuity over large tracts, as well as the constancy of the 

 order of their succession. Every student should trace one or two 

 formations through the country at an early stage in his work. 



By means of these comparative observations, begun by Mr. W. 

 Smith in 1790, and continued with unabated zeal by others, the 

 whole series of English stratified rocks has been ascertained, and 

 arranged in tabular order; and the geologists of England have, in 

 consequence of the completeness, development, and succession of strata, 

 furnished to the rest of the world a standard of comparison, by which 

 to determine how far the laws of stratification disclosed in this island 

 are applicable to other countries. 



Strike. The direction in which the plane of a stratum extends 

 through a country is termed its strike. This direction is the inter- 

 section of the plane of a stratum with the plane of the horizon, and 

 is a property of an inclined plane which is determined exclusively 

 by the direction of dip. The direction of the strike is therefore 

 always at right angles to the direction of the dip. Thus if the dip 

 is to the north or south, the strike must be east and iccst. The direc- 



VOL. I. E 





