Palaeontological Speculations —Gratacap. 209 
ment de la terre. des barriéres terrestres et marines qui ont 
mis obstacle a |’ extension des faunes riveraines.” 
That position and accidents of environment change form, 
not to ultra specific examples, but to extreme variations is well 
shown in Purpura lapillus. In sheltered coasts this protean 
shell becomes lengthened with revolving lines, upon veined or 
colored rock it shows color bands, both broad and narrow, in 
exposed situations it has a tapering spine and long aperture, 
in very sheltered places it again becomes lengthened, robust 
and with irregular surfaces, in exposed sites with small food 
supply it is small, in exposed sites with fair food supply it is 
small with depressed spine, and cancellated, on flat beds at low 
water long, sculptured, with a large last whorl, in shelters un- 
der boulders with good food supply it is sculptured, on oyster 
beds it is sculptured with spinulose fringes, again exposed, it 
shows small elevated ridges, in very sheltered places with 
abundant food they become long and smooth, again in very 
exposed positions with poor food supply they are small, some- 
what distorted, but in similar spots with abundant food supply 
they become normal and turbinate, others are shouldered and 
small, and lastly in sheltered areas with poor food supply they 
are small with prominent revolving ridges. 
Variations of this kind simply illustrate how more widely 
contrasted conditions might, in the lapse of a long time, pro- 
duce much more sharply defined differences. It would seem 
assumed by modern naturalists that however stationary life 
seems to day, in geological time evolution, or a ceaseless or- 
ganic impulse to differentiate types, and introduce new groups, 
controlled invincibly the seething currents of animal activity. 
Provincial faunas were thus originated, or as Dr. Welles 
has expressed it, “this type of development was, of course, 
brought about by the greater or less isolation of great shallow 
water tracts in different parts of the world, in each of which 
the evolution of the life progressed along its own peculiar 
lines, molded by the particular environmental conditions which 
obtained in each tract or province.” 
But are we not permitted to assume that if evolution acted 
upon one separated section of a cosmopolitan fauna it would 
act upon all other separated portions at the same’ time, and 
that if conditions were very much alike in these two separated 
