PRINCIPLES OF GEOLOGY. 



vations in distant countries : without doubt there is such conformity. 

 The series of strata in Yorkshire, taken in a general way, is the following; 

 chalk, gault?, Kimmeridge clay, coralline oolite, calcareous grit, Oxford 

 clay, Kelloways rock, cornbrash, the Bath oolite rocks, lias, red marl 

 and sandstone, magnesian limestone, coal series, mountain limestone, and 

 slate rocks. The series in the south of England is precisely accordant, 

 except that the magnesian limestone is there deficient, and that the 

 Kimmeridge clay is covered by some strata which do not reach into 

 Yorkshire. Besides, we find the Yorkshire strata actually united with 

 those of the same name in other parts of England, so that there can be 

 no doubt of the general continuity of the strata, and of constancy in their 

 order of succession. The same conclusion is upheld by independent 

 research in foreign countries. There, as in England, it is demonstrated, 

 that, to as great a depth as can be accurately examined, various rocks are 

 laid on one another, in a certain consecutive series, by which it is not 

 difficult to assign to each its unvarying place in the scale ; and that these 

 rocks are not formed in insulated patches, but in widely-extended strata, 

 which hold their courses across provinces and kingdoms. 



This encourages us to inquire whether there be not some general 

 analogy of the rocks, not only across islands and kingdoms, but even 

 across whole continents ; for if this should prove to be the case, we shall 

 be enabled to propose general laws of structure, applying equally to 

 every part of the globe. For the purpose of this comparison, we must 

 not think to employ the characters of individual rocks, however remark- 

 able they may appear, but we must group together analogous formations, 

 and look only on the greater features of nature. We must consider the 

 physiognomy of the earth, and, amidst many local variations, trace the 

 lines of general agreement. 



Reviewing the series of British rocks, we shall observe three great 

 divisions, of which two are extremely obvious ; the rocks of the moun- 

 tains and the strata of the plains : the third division possesses, perhaps, 

 quite as definite characters, but they are not manifested without more 

 research. The mountainous regions of Britain are composed of hard, 



