DOCTRINE OF GEOLOGICAL CONTINUITY. 275 



deposits absolutely synclironous as regards the time of their deposition, 

 and veiy little removed from one another in actual distance, and yet 

 containing, upon the whole, entirely distinct groups of organic 

 remains. This arises from the fact that the marine faunse of the 

 Ked Sea and Mediterranean belong to diiferent zoological provinces ; 

 and the Isthmus of Suez constitutes an impassable obstacle to their 

 inter-migration. We learn, therefore, from this, that owing to the 

 existence of geographical barriers, it is possible for contemporaneous 

 formations, to be found in close contiguity, in a single region, and 

 yet to contain very different fossils. 



We are now in a position very briefly to discuss the question of 

 what may be called "geological continuity." As is well known, the 

 entire series of sedimentary or fossiliferous rocks admits of a natural 

 division into a certain number of definite rock-groups or "formations," 

 each of which is characterised by a peculiar and distinctive assemblage 

 of fossils, constituting the "life" of the "period," in which the forma- 

 tion was deposited. The older geologists held, what, perhaps, every- 

 one would at first sight be tempted to think, that the close of each 

 formation was signalised by a general destruction of all the forms of 

 life characteristic of the period, and that the commencement of each 

 new formation was accompanied by a creation of a number of new 

 forms, destined to figure as the characteristic fossils of the same. 

 This theory, however, not only invokes forces and processes which it 

 can in no way account for, but overlooks the fact that most of the 

 great formations were separated by lapses of time unrepresented by 

 any deposition of rock, and yet as long or longer than the whole time 

 occupied in the production of the formation itself. Indeed, we are 

 compelled to admit that what we call the great "formations" are 

 purely artificial divisions, rendered possible by the gaps in our 

 knowledge only, and that if we had a complete series of rock-groups, 

 we could have no such divisions. 



Now-a-days, then, most geologists hold that there was no such 

 sudden destruction of life at the close of each great geological epoch, 

 and no such creation of fresh forms at the commencement of the 

 ensuing period. On the contrary, they hold that there is a geological 

 "continuity," such as we see in other departments of nature ; and 

 that the lines which we draw between the great formations merely 

 •mark periods of time, the rocks deposited in which are at present 



