SILLIMAN'S INTRODUCTION. 6 



perished, while new races have been called into being, and in their 

 turn have ceased to be, in order to give room to other families, 

 requiring, perhaps, new physical conditions. 



Thus we travel onward in time, and upward in the order of 

 deposition, through races whose species are entirely extinct, until 

 we arrive at the periods that approximate to our own times, when 

 first, similar beings to those that now inhabit the earth begin to 

 appear, and finally to graduate into those of the present day. Now 

 it is obvious, that to judge intelligently of extinct races of animals 

 and vegetables, it is requisite to pass in review the entire organic 

 creation, both of ancient and modern date ; not only of the ter- 

 restrial animals that, in early times, walked the earth, of the fishes 

 and amphibia that swam in the waters, of the birds, insects, and 

 winged reptiles that soared in the air, and of the plants that adorned 

 the new-born islands and emerging continents, and which, as well as 

 the animals, are now entombed in rocks and mountains ; but, we 

 must be familiar, also, with the races which, at this moment, fill the 

 world with animation and beauty, for they are our living standards 

 of comparison. In short, we must be well acquainted with both 

 natural history and comparative anatomy. 



If such be the circle of sciences preliminary or auxiliary to 

 geology, it may well draw from us the desponding exclamation, 

 Who then is sufficient for these things ? We may perhaps reply, no 

 unassisted individual ! Science is formed by the joint labours of 

 many minds. Different cultivators bring in the rich tribute of 

 the fields they have tilled and reaped, and a master mind disposes 

 them in order, and draws from them the requisite conclusions to 

 construct a system, or, at least, to furnish its most important 

 elements. 



3. Hank among the Sciences. — This very general sketch of 

 the relations which geology sustains to the collateral sciences, is 

 sufficient to evince its high dignity, and to vindicate its strong 

 claims to our serious attention. As a science, its date is modem ; 

 but this is also true of all the physical sciences, among which 

 geology is a younger sister. Although it is rapidly advancing, and 

 is, therefore, not perfect, but progressive, it is still a science ; and 

 in this sense, which of the physical sciences is perfect ? * In this 



* "To boast of a stability of opinion in Geology, is to boast of an extreme indolence 

 of mind ; it is to remain stationary in the midst of those who go forward."— Baron 

 Humboldt. 



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