140 GEOLOGICAL RECONNOISSANCE 



attention to this, the geologist would dispense with one of his principal 

 aids in drawing important practical inferences and proofs corroborative of 

 his assertions. This branch of the survey might appear to some, without 

 due reflection, a matter of little importance ; but when we consider that 

 it is the surest and safest guide to the identification of all the formations 

 of sedimentary origin, and even of the individual members of such for- 

 mations, as for instance, the beds of coal, we discover that it is the index, 

 the criterion, the sign, the " divining rod," if I may so express it, which is 

 to lead the geologist in his search after mineral wealth. 



I cannot present the practical importance, as well as the interest con- 

 nected with the study of these relics of bygone ages, in a stronger light 

 than by inserting here an extract from my report of the surveys made in 

 behalf of the United States, some years since, in the North-west. 



" The study of the organic remains of rocks is, indeed, a most beautiful, a 

 most fascinating research. What can be more extraordinary: that we, 

 the generation of the nineteenth century, should exhume from out the 

 hard substance of the solid rocks, the delicate forms of organic beings of 

 bygone ages, and display to the wondering eye of the naturalist, even 

 their minute anatomical details ? And this, not alone of races which 

 inhabited this earth in times immediately preceding the human epoch; we 

 are even permitted to contemplate, and restore to our perceptions, the 

 very fishes, mollusks, and corals, that swarmed in the carboniferous seas 

 millions of ages ago. The animal matter composing their tissues and 

 bones is indeed gone, but the simultaneous mineral infiltrations preserve 

 a perfect counterpart. We can depict those remarkable and elegant forms 

 of vegetation which constituted the forests, that fringed the shores of that 

 same treacherous and overwhelming ocean. We seize them in the very 

 act of uncoiling their frond, and unfold to the admiring gaze of the 

 botanist, that luxuriant canopy of foliage that once waved in the sea- 

 breeze nurturing their stems. We accomplish even more than this : we 

 can read the records of myriads of the lower orders of animals, that date 

 their existence yet further back than the times that gave growth to trees, 

 now stored up as mineral fuel in the bowels of the earth — to times at least 

 as long prior to the coal formation, as that geological era is antecedent to 

 the present time ; we can assign to each its place in the zoological systems, 

 and fill up the gaps in the existing orders of the animal and vegetable 

 kingdoms. 



" To think that we, at this day, can demonstrate the structure of the eye 

 of some of these — the most ancient races — and even count the lenses by 

 which light was concentrated to the optic nerve, is truly astonishing ! Is 



