Till-; SUCCESSION OF STll.VI 1! IKH Ko.'KS 3 



But, it may be asked, when two such district* have been inde- 

 pendently investigated, how are we to con-Hat, tin- two tables of 

 strata, and ascertain which rocks or rock-groups were appr 

 match- contemporaneous? It is here that a knowledge of fossils 

 (Paleontology) conies to our aid, and enables iw to identify rocku 

 by their fossil contents, so that strata in different district* and of 

 different lithological characters may be included in the same natural 

 group or system, because they contain the same or closely similar 

 species of fossils. This was the principle discovered and applied 

 at the beginning of last century by Dr. William Smith, who is 

 often called the Father of British Geology, and who was certainly 

 the founder of that branch of the science which is the subject of 

 the present volume. 



The book in which Smith recorded his discovery of the strati- 

 graphical use of fossils was entitled Strata identified by Oryaniud 

 Fossils, and was published in 1816. He had previously made 

 out the succession of the strata which occur near Bath, and had 

 observed that each well-marked group of beds contained a special 

 assemblage of fossils. As his acquaintance with English rocks be- 

 came larger he noticed that there was a similar succession elsewhere, 

 and thus (in the words of his nephew and biographer l ) " he 

 inferred that each of the separate periods occupied in the formation 

 of the strata was accompanied by a peculiar series of the forma of 

 organic life, that these forms characterised those periods, and that 

 the different strata could be identified in distant localities and 

 otherwise doubtful cases by peculiar embedded organic remains." 



The experience of subsequent observers confirmed and established 

 this inference, which has become a guiding principle in strati - 

 graphical geology. Further research, moreover, has brought out 

 the more definite conclusion that there has been a continuous 

 succession of life-forms, that species and genera and families, and 

 even whole orders of beings, have come into existence, have flourished, 

 and have then gradually died out, never to recur. It is this non- 

 recurrence of species which gives a special value to fossils as a test 

 of age and as a means of correlation. The same kind of rock has 

 been formed again and again during the history of the world, but 

 when once a species has died out it has never appeared again. 



It must not be supposed, however, that the stratigraphies! 

 succession of rocks presents us with a complete record of the 

 history of the earth, or that it will ever supply us with examples 

 of all the species which have lived upon the earth's surface. On 

 the contrary, the records preserved to us are very incomplete, and 

 many pages are wanting in every chapter of the great volume, so 

 1 Memoirs of William Smith, by John Phillips, F.R.8,, 1844. 



