108 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Before leaving this subject, there is another interesting* topic of in- 

 quiry : why such a beautiful series of vertebrate remains should be so 

 perfectly preserved in this lake deposit, and yet the remains of other 

 forms of animal and vegetable life be almost entirely absent. The sedi- 

 ments seem to be peculiarly adapted to the preservation of a full series 

 of documents bearing upon the history of those times. And yet in the 

 older beds, where the mammalian remains are most abundant, only one 

 small species of snail, a land shell, is found preserved. Where is the 

 evidence of the swarms of fishes that must have filled the streams and 

 lakes of that time % Of the vegetable life, if any existed, only now and 

 then a fragment of silicified wood is found, and that, too, in the latest 

 deposits. I am prepared to believe that the broad plains were, even at 

 the time of the existence of these animals, as treeless as at present, yet 

 I am quite unprepared to explain the almost entire absence of vegetable 

 remains. We know that fresh- water shells, much like those existing in 

 the little clear streams of the present time, as well as some remains of 

 fishes, are found in some limestones on the summits of hills near Pinos 

 Spring on the northern rim of the lake. 



Another interesting question occurs to me in this connection, how 

 was it that a complete fauna, comprising more than forty species of ani- 

 mals, was introduced upon the earth, lived through its legitimate period, 

 entirely perished or was swept out of existence, and an entirely new T 

 fauna, comprising about the same number and variety, was again intro- 

 duced in the same region? It, too, lived out its period of existence, 

 which must have been hundreds of thousands of years, and yet every 

 one of this group of animals disappeared from the globe, leaving no- 

 thing behind to tell the tale but fragments of their bony skeletons, acci- 

 dentally enveloped in the sediment at the bottom of an estuary or lake. 



It will be seen at a glance that this is a fruitful topic for speculation, 

 and I leave it with the reader. Some of the species of animals found 

 in the latest deposits seem to have lived very nearly up to our present 

 period. The horns of a deer and the bones of a sand-hill crane have 

 such a modern aspect that the thought arises, where was man when 

 these animals were roaming over this region ? Eecent investigations 

 show quite conclusively that man was an inhabitant of Europe cotem- 

 poraneously with many of the extinct animals of the quartern ary period, 

 but it is doubtful whether we have ever found any evidence that he lived 

 at a very remote period on this continent. Indeed, so far as we know 

 at present, the West is singularly silent as to the existence of man in 

 what are now understood as pre-historic times. 



But let us move our camp further south and toward the Platte Valley 

 again, and on our way just glance at a desolate and almost barren but 

 interesting region called the Sand Hills. They cover an area of about 

 twenty thousand square miles on both sides of the Niobrara Biver, and 

 are composed of loose, moving sand, which is blown by the winds into 

 round, conical hills with considerable regularity. As far as the eye can 

 reach the surface presents the appearance of a multitude of round tops, 

 some of them scooped out by the whirling winds so as to resemble era 

 ters. These sand hills have been from time immemorial a favorite resort 

 of the buffalo, which feeds upon the scanty but very nutritious grasses 

 in the little valleys and intervals among these hills. There is, for the 

 most part, an abundant supply of water in the little lakes that are scat- 

 tered throughout this region. Some of them are alkaline in the highest 

 degree, and the fresh can be detected from the salt lakes by the pres- 

 ence or absence of vegetation in and around the borders. These hills 

 are sometimes protected from the winds by a considerable giowth of 



