78 PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



intervene between two littoral faunas, recent researches seem to show 

 that the littoral forms of life may wander into such tracts, and 

 eventually, perhaps, cross them, without undsrgoing extreme or pro- 

 found modification. In this way, I think, we may account for the 

 important fact so prominently brought into view by Dr. Blanford, 

 that marine life-provinces are and always must have been less 

 restricted in area, and less sharply cut off from one another, than 

 terrestrial provinces. 



With the clear recognition of this principle there falls to the 

 ground one of the most frequently urged objections to the Uniformi- 

 tarian doctrines — that, namely, which is based on the supposed 

 differences in geographical distribution in ancient times as compared 

 with the present. We have been in the habit of comparing ancient 

 marine distribution with modern terrestrial distribution. I have 

 always doubted whether there is any evidence to show that the 

 marine life-provinces of Silurian or Carboniferous times were of 

 greater extent than those of the present day. 



I believe that the doctrine that strata can be identified by the 

 organic remains which they contain is as sound as when it was first 

 enunciated by William Smith ; but the problems of stratigraphical 

 palaeontology, as they now present themselves to us, are infinitely 

 more complicated than they could possibly have seemed to him. In 

 every fauna and fiora which we are called upon to study we have 

 to resolve a function of three variables, these being environment, 

 space, and time. Only after the most careful investigation, in the 

 first place, of the complicated effects produced by the varied condi- 

 tions which we group together under the term environment — tem- 

 perature, food, absence of enemies, and the innumerable influences 

 which, as we now know, determine the existence and affect the 

 multiplication of living beings — and by the thorough study, in the 

 second place, of the laws of geographical distribution of plants and 

 animals, can we hope to eliminate the effects due to environment 

 and position, and arrive at the conclusion of what must be ascribed 

 to time. 



The task will be long, the work to be done arduous, and the 

 efforts to be made prodigious and sustained ; but the result is one 

 which is not hopeless and unattainable, or, indeed, even doubtful. 

 But let us by all means remember that the real work is really only 

 just commenced, and that we are very far indeed from our goal. 



One of the greatest sources of danger to the progress of geological 

 knowledge at the present day is the impatience which is so fre- 



