324 GEOLOGICAL SURVEY OF THE TEERITORIES. 



sboiiid be but just liatclied, and for this and other reasons it has been 

 conchided that this •• ancient mariner" is one of those forms not uncom- 

 mon in old days, whose incompleteness in some respects points to the 

 truth of the belief that animals have assumed their modern perfections 

 by a process of growth from more simple beginnings. 



^ The Cretaceous ocean of the West was no less remarkable for its fishes 

 than for 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. 



Yertebme and other fragments of these species project from the worn 

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

 midable as well as the most abuudant of these. It is the one whose 

 bones most frequently crowned knobs of shale, which had been left 

 standing amid surrounding destruction. The density and hardness of 

 the bones shed the rain oil" on either side, so that the radiating gutters 

 and rapines finally isolated the rock mass from that surrounding. The 

 head was as long or longer than that 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 irregular size. At 

 certain distances in each jaw they projected three inches above tue gum, 

 and were sunk one inch into the jaw margin, being thus as long as the 

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

 on each side of the middle of the front. This fish is known as Porfheus 

 molossus. Cope. Besides the smaller fishes, the reptiles no doubt sup- 

 plied the demands of his 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 the Arctic Sea. The continued elevation of both eastern 

 and western shores contracted its area, and when ridges of the sea-bot- 

 tom reached the surface, forming long, low bars, parts of the water-area 

 were inclosed and connection with salt-water prevented. Thus were 

 the living beings imprisoned and subjected 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. 

 With the death of any considerable class the balance of food-supply 

 would 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 fate ; the last one 

 caught by the shifting bottom among shallow pools, from which liis 

 exhausted energies could not extricate him. 



Part II.— GEOLOGY. 



The geology of this region has been very partially explored, but ap- 

 pears to be quite simple. The following descriinion of the section along 

 the lino of the Kansas Pacific Railroad will ])robably a]>ply to similar 

 sections north and south of it. The formations referable to the Creta- 

 ceous period on this line are those called by Messrs. Meek and Hay 

 den the Dakota. Benton, and Niobrara groups, orXos. 1. 2, and 3. Ac- 

 cording to Leconte,* at Salina, one hundred and eighty-five miles west 

 of the State line of Missouri, the rocks of the Dakota group constitute 



^ Xotes on the Geology of the Siirvey for the Extension of the Union Pacific Road, 

 Eastern Division, from the Smokv Hill to the Rio Grande. Bv John L. Lecoute, M. D., 

 Philadelphia, 1S6S. 



