872 THE SPIRAL SHELLS [ch. 



a very simple matter of mechanical analysis. The coarseness or 

 fineness of the sediment on the sea-bottom is a measure of the 

 current: where the current is strong the larger stones are washed 

 clean, where there is perfect stillness the finest mud settles down; 

 and the light, fragile shells of the Foraminifera find their appropriate 

 place, like every other graded sediment in this spontaneous order 

 of levigation. 



The theorem of Organic Evolution is one thing; the problem of 

 deciphering the lines of evolution, the order of phylogeny, the degrees 

 of relationship and consanguinity, is quite another. Among the 

 higher organisms we arrive at conclusions regarding these things 

 by weighing much circumstantial evidence, by dealing with the 

 resultant of many variations, and by considering the probability 

 or improbability of many coincidences of cause and effect; but 

 even then our conclusions are at best uncertain, our judgments are 

 continually open to revision and subject to appeal, and all the proof 

 and confirmation we can ever have is that which comes from the 

 direct, but fragmentary evidence of palaeontology*. 



But in so far as forms can be shewn to depend on the play of 

 physical forces, and the variations of form to be directly due to 

 simple quantitative variations in these, just so far are we thrown 

 back on our guard before the biological conception of consanguinity, 

 and compelled to revise the vague canons which connect classification 

 with phylogeny. 



The physicist explains in terms of the properties of matter, and 

 classifies according to a mathematical analysis, all the drops and 

 forms of drops and associations of drops, all the kinds of froth and 

 foam, which he may discover among inanimate things; and his 

 task ends there. But when such forms, such conformations and 

 configurations, occur among living things, then at once the biologist 

 introduces his concepts of heredity, of historical evolution, of suc- 

 cession in time, of recapitulation of remote ancestry in individual 

 growlh, of common origin (unless contradicted by direct evidence) 

 of similar forms remotely separated by geographic space or geologic 

 time, of fitness for a function, of adaptation to an environment, of 

 higher and lower, of " better " and " worse." This is the fundamental 



* In regard to the Foraminifera, "die Palaeontologie lasst uns leider an Anfang 

 der Stammesgeschichte fast ganzlich im Stiche," Rhumbler, op. cit. p. 14. 



