| Summary: | And Early Explorations 507 tablished primarily as the east boundary line of Montana on the 27th degree of longitude west of Washington, the corners, established at mile intervals, being either of stone or native wood, the latter either of Cottonwood, elm or pine. This line was not intended to be on the 104th degree of west longitude but on the 27th meridian west of Washington. There is a difference of 03' 02.3" in longitude between even degrees of these two meridians, the Washington meridian being the farther west. Uncertainty in the longitude of the initial position and errors in the field surveys were the causes of the errors now known to exist in the position and bearing of the line. It was run due north on the 27th degree of longitude west of Washington, D. C, but does not necessarily coincide with any particular section or half section line. LANDSCAPE GEOLOGY There have been many ages or periods in the annals of time since the world began, the Archaean or Age of Landscapes, the Silurian, when all life on the globe was invertebrates, Devonian, Age of Fishes, Carbeniferous or Age of Coal Plants or Acrogens, Mesozoic Age of Reptiles, Tertiary Age of Mammals, Quarter- nary Age of Man, and the Age of Ice or the Glacial Period. The Glacial Period was the last great Geological Period before that in which man lives the period of written history. During the Glacial Period a great sheet or mantle of ice covered nearly all of North America. A great lobe of this glacier known as the Dakota Glacier extended from Manitoba into South Dakota on the east side of the Missouri River. When this sheet began to melt it gradually drifted south and a little east. This great ice plow cut down the hills of the old landscape and filled in with drift. At the beginning all landscapes were sea bottom. As the great ice sheet gradually moved southward it carried large deposits wherever the ice melted which are called Moraines. There are four kinds of Moraines, Terminal, Lateral, Medial, and Ground. These deposits also washed down and covered the level and rolling prairies portion of the state with a mantle of "drift" of a slight depth at the Missouri River to over 300 feet in the Red River Valley. ' - With the melting of the great ice sheet, Glacial Lake Agassiz Scanned with a Zeutschel Zeta book scanner at 300 dpi. Edited with Multi-Page TIFF Editor.
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