50 



The Cretaceous ocean of tlie West was no less remarkable tbr'its fishes 

 tliau tor its reptiles. Sharks do not seem to have been so common as in the 

 old Atlantic, but it swarmed with large predaceous forms related to the 

 salmon and saury. 



VcrtebrjB and other fragments of these species project from the worn 

 limestone in many places. I will call attention to perhaps the most formida- 

 ble as well as the most abundant of these. It is the one whose bones most 

 frequently crowned knobs of shale, which had been left standing amid sur- 

 rounding destruction. The density and hardness of the bones shed the rain 

 off on either side, so that the radiating gutters and ravines finally isolated the 

 rock mass from that surrounding. The head was some inches longer tlian 

 tliat of a fully-grown grizzly bear, and the jaws were deeper in proportion to 

 their length. The muzzle was shorter and deeper than that of a bull-dog. 

 The teeth were all sharp cylindric fangs, smooth and glistening, and of irreg- 

 ular size. At certain points in each jaw they projected three inches above 

 the gum, and were sunk one inch into deep pits, being thus as long as the 

 fangs of a tiger, but more slender. Two pairs of such tangs crossed each 

 other on each side of the end of the snout. This fish is known as Forthcus 

 molossus, Cope. Besides the smaller fishes, the reptiles no doubt supplied the 

 demands of its appetite. 



The ocean in which flourished this abundant and vigorous life was at last 

 completely inclosed on the west by elevations of sea-bottom, so that it only 

 communicated with the Atlantic and Pacific at the Gulf of Mexico and th(; 

 Arctic Sea. The continued elevation of both eastern and western sliores 

 contracted its area, and when ridges of the sea-bottom reached the surface, 

 Ibrming long, low bars, parts of the water-area were inclosed, and connection 

 with salt-water prevented. Thus were the living beings imprisoned and sul)- 

 jected to many new risks to life. The stronger could more readily capture 

 the weaker, while the fishes would gradually perish through the constant 

 freshening of the water. Willi the death of any considerable class, the l)al- 

 ance of food-supply woukl be lost, and many larger species would disappear 

 from the scene. The most omnivorous and enduring would longest resist the 

 approach of starvation, but would finally yield to inexorable fiite ; the last one- 

 caught by the shifting bottom among shallow pools, from which his exhausted 

 energies could not extricate him. 



