A HISTORY OF SCIENCE 



fossils is always the same in any vertical series of strata 

 in which they occur. That is to say, if fossil A under- 

 lies fossil B in any given region, it never overlies it in 

 any other series ; though a kind of fossils found in one 

 set of strata may be quite omitted in another. More- 

 over, a fossil once having disappeared never reappears 

 in any later stratum. 



From these novel facts Smith drew the common- 

 sense inference that the earth had had successive pop- 

 ulations of creatures, each of which in its turn had be- 

 come extinct. He partially verified this inference by 

 comparing the fossil shells with existing species of sim- 

 ilar orders, 'and found that such as occur in older 

 strata of the rocks had no counterparts among living 

 species. But, on the whole, being eminently a practical 

 man, Smith troubled himself but little about the in- 

 ferences that might be drawn from his facts. He was 

 chiefly concerned in using the key he had discovered 

 as an aid to the construction of the first geological map 

 of England ever attempted, and he left to others the 

 untangling of any snarls of thought that might seem 

 to arise from his discovery of the succession of varying 

 forms of life on the globe. 



He disseminated his views far and wide, however, in 

 the course of his journeyings quite disregarding the 

 fact that peripatetics went out of fashion when the 

 printing-press came in and by the beginning of the 

 nineteenth century he had begun to have a following 

 among the geologists of England. It must not for a 

 moment be supposed, however, that his contention re- 

 garding the succession of strata met with immediate 

 or general acceptance. On the contrary, it was most 



