THE SILURIAN BEACH. 
35 
cussions concerning the transition of species are 
carried on, is mainly owing to an ignorance of the 
conditions above alluded to. My own personal 
observation and experience in these matters have 
led me to the conviction that every geological 
period has had its own representatives, and that 
no single species has been repeated in successive 
ages. 
The laws regulating the geographical distribu- 
tion of animals, and their combination into dis- 
tinct zoological provinces called faunae, with defi- 
nite limits, are very imperfectly understood as 
yet ; but so closely are all things linked together 
from the beginning till to-day that I am con- 
vinced we shall never find the clew to their 
meaning till we carry on our investigations in 
the past and the present simultaneously. The 
same principle according to which animal and 
vegetable life is distributed over the surface of 
the earth now, prevailed in the earliest geological 
periods. The geological deposits of all times 
have had their characteristic faunas under vari- 
ous zones, their zoological provinces presenting 
special combinations of animal and vegetable life 
over certain regions, and their representative 
types reproducing in different countries, but un- 
der similar latitudes, the same groups with spe- 
cific differences. 
Of course, the nearer we approach the begin- 
