252 GEOLOGY. 



CHAPTER VII. 



QUATERNARY AGE. GLACIAL PERIOD TO THE 

 LOESS. SUPERFICIAL DEPOSITS. 



Opening of the Glacial Period. A period of great humidity and cold.^ 

 Glaciation of the Plains. Direction of the Glacial Mass and thickness. Ma- 

 terials. Blue Clay, its extent and character. Eesemblance to the Till and 

 Erie Clays. Analysis. Whitish Clays. Boulder Clay. Drift Materials. 

 Description of a Section. Old Forest Bed. Extent, Character and Sections 

 Its Fossils Second Appearance of Glacial Drift. Karaes. Calcareous and 

 Silicious Materials. Section of them and General Character. Transition 

 Beds Analysis of the Calcareous Materials. Origin of these Beds. Course 

 of events to the beginning of the Loess. 



WE have seen at the close of the last chapter how the Pliocene 

 epoch closed its remarkable history. Its closing centuries 

 were the opening ones of the Quaternary Age. The continent 

 had sunken towards the south and was rising towards the north. 

 Where once had been the floor of a lake of the plains had now su- 

 pervened a very great change of level. The southern end of the 

 once great Pliocene lake was now, at least, at the level of the sea, and 

 the northern end was 7,000 feet higher. The plains were dessi- 

 cated before the Pliocene had entirely passed away. King has 

 given reasons to suppose that this was even the case with the great 

 lake of the basin region that between the Pliocene and Quater- 

 nary this region was dried up. Following this condition of dryness 

 was one of great humidity and a much lower temperature than the 

 present. The snows of winter accumulated too rapidly finally to 

 be removed by the summer warmth. Eventually the plains ot 

 Nebraska became glaciated and were covered by a thick mantle of 

 ice. This was the first, or glacial period of the Quaternary. In 

 this respect Nebraska agrees with the Quaternary in eastern Amer- 

 ica, where Dana divides the age into the Glacial period, the Cham- 

 plain or low level period, and the Terrace or recent period. These 

 divisions are not strictly applicable to Nebraska. Here we have a 

 Glacial, a Boulder Clay, or true Drift, a Forest Bed, a second 

 Drift, Loess and Terrace period. These divisions are more or less 

 clearly outlined in our superficial geology. 



