DISTRIBUTION IN TIME. 157 



of the period in which the formation was deposited. It is 

 a matter of importance to understand clearly how far these 

 subdivisions are natural, and what value we may attach to 

 them. The older and very natural view held 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 the creation of a number of new forms. On the more 

 modern view, it is held that the great formations, and many 

 of the minor subdivisions, are separated by longer or shorter 

 lapses of time not represented by any deposition of rock in 

 the area where the formations in question are in contact. 

 Upon this view we have 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 lines of demarcation. 



It is unnecessary to consider here why it is that we can 

 never hope to find a complete series of intermediate rock- 

 groups by which any two great formations might be linked 

 together. It is sufficient to say that we may well have the 

 strong tonviction that such intermediate deposits have at 

 one time existed, or must still exist, whilst there are per- 

 fectly valid reasons for the belief that we can never know 

 more than fragments of them. 



Most modern geologists, then, would hold that there is a 

 geological " continuity," such as we see in other departments 

 of nature. There can have been in reality no break in the 

 great series of stratified deposits ; but there must have been 

 a complete "continuity" of life and deposition from the 

 Laurentian period to the present day. There was, and could 

 have been, no such continuity in any one area ; but it is 

 inconceivable that the chain should have been snapped at 

 one point and again taken up at another wholly different 

 one. The links of the chain may, indeed must, have been 

 forged in different places, but its continuity must neverthe- 



