226 THE DAWN OP LIFE. 



with Foraminifers, extending all the way from the 

 Laurentian to the present time, I can imagine nothing 

 more interesting than to compare the whole series, 

 with the view of ascertaining the limits of descent with 

 variation, and the points where new forms are intro- 

 duced. We have not yet such a series, but it may be 

 obtained ; and as Foraminifera are eminently cosmopo- 

 litan, occurring over vastly wide areas of sea-bottom, 

 and are very variable, they would afford a better test 

 of theories of derivation than any that can be obtained 

 from the more locally distributed and less variable ani- 

 mals of higher grade. I was much struck with this 

 recently, in examining a series of Foraminifera from 

 the Cretaceous of Manitoba, and comparing them with 

 the varietal forms of the same species in the interior of 

 Nebraska, 500 miles to the south, and with those of 

 the English chalk and of the modern seas. In all 

 these different times and places we had the same spe- 

 cies. In all they existed under so many varietal forms 

 passing into each other, that in former times every 

 species had been multiplied into several. Yet in all, 

 the identical varietal forms were repeated with the 

 most minute markings alike. Here were at once 

 constancy the most remarkable and variations the 

 most extensive. If we dwell on the one to the exclu- 

 sion of the other, we reach only one-sided conclusions, 

 imperfect and unsatisfactory. By taking both in con- 

 nection we can alone realize the full significance of the 

 facts. We cannot yet obtain such series for all geolo- 

 gical time ; but it may even now be worth while to 



