A PROBLEM IN EVOLUTION 429 



from which it came. To reach them, a path had to be cut into the 

 face of the cliff, and the rocks overlying the beds removed with dyna- 

 mite, or with pick and bar ; an operation not without some danger from 

 rocks that from time to time fell from the crumbling cliffs above. 

 Twice, without warning, fragments weighing some fifty pounds each 

 fell at our feet, knocking the tools, from our hands; and where they 

 came from there were other loose ones, at least ten times as large. Our 

 attention was reluctantly, but impartially, divided between the main- 

 tenance of a precarious footing on the face of the sweltering cliff, the 

 threatening rocks overhead, and the treasures at our feet. 



The bed was not extensive, but it proved to be literally teeming 

 with these extraordinary animals (Bothriolepis canadensis), and by 

 good fortune they were in a remarkably complete and instructive state 

 of preservation; more so, perhaps, than any other fossils found here- 

 tofore (Fig. 6). 



The bed had apparently formed the bottom of a shallow, brackish 

 water-pool in which fern-like water plants had been growing, and 

 where many millions of years ago, with the rise and fall of the tides, 

 these specimens had been tiapped, together with other species of ostra- 

 coderms and several kinds of true fishes. 



The soft mud on the bottom of the pool was now turned into a 

 fine-grained, sandy limestone, and in it the fossilized animals were 

 preserved in the very attitudes they had assumed when they ceased to 

 struggle out of the enclosure. One, in its death agony, had plunged 

 into the mud with sufficient force to remain there, head down, in a 

 vertical position. Others were arranged in horizontal series, uniformly 

 headed in a northeast direction. Their heads were turned against a 

 gentle current of water, as was shown by the fact that the tops of all 

 the ferns were pointed in nearly the opposite direction. 



Many of these specimens were so well preserved that the shape of 

 the whole body, and many details on its external surface, could be 

 readily observed; the general character and location of the principal 

 sense organs, jaws, gills, stomach, anus and genital openings ascer- 

 tained; and the neural and haemal surfaces identified. It was also 

 possible to determine, beyond reasonable doubt, the mode of locomotion, 

 the mode of feeding and the nature of the food. 



Of course this message from a remote past was not off-hand legible. 

 After the scores of specimens were safely housed in the laboratory, it 

 required nearly three years to chisel and scratch and brush away the 

 rocky matrix in which they were imbedded, and after that many speci- 

 mens had to be cut into serial sections with a diamond saw, and the 

 sections polished and varnished to show the arrangement of the internal 

 organs. 



