284 KEY TO TERRESTRIAL HISTORY 



The little that we know about the habits of the 

 Ammonites, and indeed it is not much, points decidedly 

 to a mode of life not unlike that of the existing Nautilus, 

 which certainly could not cross deep oceans; nor is it 

 likely that the drifting of abandoned shells could explain 

 a community of species between Cutch and England, and 

 England and Chili. 



The more we consider the matter the more do we seem 

 driven to admit that a continuous distribution of such 

 forms as Ammonites must be dependent on a more or 

 less continuous shore-line. 



The Graptolites are in a different case : there is clear 

 evidence that some of them were provided with a 

 pneumatophore, and that, consequently, they were floating 

 organisms. Some may, as Professor Lapworth suggests, 

 have been attached to floating seaweed, and some may 

 even have been propagated through the intermediation of 

 jelly-fish, as happens with many modern Hydrozoa. 



Thus, then, either by the influence of a particularly 

 favourable distribution of land and sea, or by a special 

 mode of life, we are enabled to understand the peculiarly 

 wide distribution which is characteristic of the fossils 

 used in correlating geological horizons. Is it possible to 

 proceed further, and throw some light on the rapidity with 

 which these forms seem to have succeeded in occupying 

 the globe ? 



There is abundant evidence to show that many of the 

 activities of the earth were enhanced in past time. Even 

 its rotation on its axis is a changing quantity. About 56 

 millions of years or so ago, as Professor George Darwin 

 informs us, the length of the day was only some ten hours 

 instead of twenty-four, and I suppose that 26 millions of 

 years back, which brings us within the limits of the 

 sedimentary record, it would be about twenty hours, 

 so that a point on the equator would then have 



