12 PICTURESQUE SKETCHES 



accurately recorded ; and from this treasure-house of 

 facts there must soon be derived a theory that will com- 

 mand attention, and a knowledge of laws not less uni- 

 versal than the law of gravitation, or the theory of the 

 solar system. Meantime I propose- in the following 

 pages to arrange some of these facts in order, and 

 so present them to notice, that, while the main re- 

 sults which they prove are plainly set before the 

 reader, he need not be deterred from considering 

 them by any too minute reference to the details of the 

 facts themselves, or the circumstances under which 

 they have been discovered or observed. 



But I must not proceed to the immediate subject 

 Avithout stating, in a very few words, the nature of 

 the arrangement that I shall follow in my descriptions. 

 In many cases the phenomena themselves, by a due con- 

 sideration of which groups of strata are distinguished, 

 will be stated and explained; but it will not always be 

 convenient to do this, and in such cases I would have 

 the reader recollect that I have not ventured to draw 

 a line of demarcation unless nature has distinctly in- 

 dicated it. These lines, however, are not all equally 

 evident. In the whole series of strata exhibited in 

 the British isles, there are, for instance, only two 

 groups so natural, so unquestionable, and so real, that 

 they render the task of classification easy and satis- 

 factory. One of these groups is again subdivided, and 

 this separation also is marked by a great change in 

 organic remains, so that we have three sets of beds, 

 which we may call respectively the Ancient, the Mid- 

 dle, and the Modern, and each of these we may con- 

 veniently look upon as denoting a lapse of time 

 which we may call an "Epoch" 



