STUDIES OF SPECIAL LACUSTRAL HISTORY. 115 



menagerie of strange and freijuently gigantic forms have been made 

 known by the labors of American paleontologists. 



Immediately preceding the " Great (Geological Winter,"' as the Glacial 

 epoch has been termed, when half of tlie North American continent was 

 sheathed in ice, there was a period of genial climate when vegetation, as 

 varied and l)cantiful as tliat of the Mississippi valley to-day, extended far 

 north and reached the vicinity of the pole itself. During different epochs 

 in this geological summer, known as the Tertiary period, vast fresh-water 

 lakes existed in the Cordilleran region, several of Avhich were far more 

 extensive than any lakes now known. In some of these vast inland seas 

 several thousand feet of sediments were laid down. In these deposits 

 we find in abundance the im})ressions of leaves that were l)lown from the 

 land, or Avashed in l)y tributary streams, and the bones of many large 

 mammals, whose homes were along the lake shores and on neighboring 

 forest-covered hills. 



All trace of the shore topography of the Tertiary lakes has disap- 

 peared, and in many instances the beds of sand, clay, and volcanic dust 

 deposited over their bottoms have been upheaved into mountain ranges, 

 and deeply dissected by erosion. Their histories can only be deciphered 

 from the records in their sediments. Their story deals largely with the 

 structure, habits, and development of vertebrate animals, and inust be left 

 to those skilled in that branch of study. 



Beyond tlie Tertiary period, and so remote from our own time that 

 humble forms of mammalian life had only just appeared on the earth, 

 Avere the Jui'assic and Triassic periods. In this Mesozoic time, or middle 

 age of the earth, lakes also existed, and in their sediments the skeletons of 

 another striking and grotesque assemblage of strange forms were pre- 

 served. The magic wand of modern science has brought forth from these 

 long-silent tomljs a wonderful })rocession of gigantic reptiles, the like of 

 which has not since existed on the eartli. 



Still nu)rc remote were the lakes and swamjis of the Carboniferous 

 I)eriod. The oldest records of air-l)reatliing vertebrates yet discovered are 

 the Ijones of reptiles found ])y Dawson in hollow-tree trunks that stood in 

 the fresh-water swamps of Nova Scotia during the time our continent was 

 green with tlie ferns and cliilHinosscs of ihcCoal jjcriod. \\'itli these bones 

 are mingled the shells of land-snails, tlic eailicsl of tlicir class yet found. 



In de[)Osits of cannel coal fornuMl in fresh-water ])ouds in the great 

 coal swamps of Ohio, Newb'iy discovered a large number of species of 

 fishes and ann)liibiaiis. in a beautiful state of presei'vation. 



