The Montana lobe of the Keewatin ice sheet

Abstract

Just south of the forty-ninth parallel and east of the Rocky Mountains is an area that is of much interest to glacialists. It is the area which lay between the Keewatin ice sheet and the mountain glaciers coming from the west. Although it has been known for nearly twenty years that the bodies of drift deposited by the ice coming from opposite directions were closely associated, little detailed field work has been done in this region. As early as 1881 Sir James Geikie prophesied that a careful study of the region would clear up many important points in glaciology. In 1885, Dr. T. C. Chamberlin and Prof E. D. Salisbury, in a reconnaissance of the region, determined roughly the course of the terminal moraine of the eastern ice sheet and obtained data concerning the character and extent of the mountain glaciation. In 1890 Mr. G. E. Culver, while a member of the military party under the command of Lieutenant Ahern, U. S. Army, gathered many data concerning the geology of the region, publishing the results of his investigations in the Transactions of the Wisconsin Academy of Sciences, in 1891. Doctor Dawson and Mr McConnell, of the Canadian Survey, have worked out the geology of the region north of the boundary line. Their reports are unusually complete, but the area to the south offers better opportunity for study, and somewhat different conclusions were reached from a study of that region. The work on which the following discussion is based was done during the field seasons of 1901, 1902, and 1903. During the first season the writer was accompanied by Mr. Bruce McLeish, then a student at the University of Chicago. The second year Mr. Porter Graves, of the Kansas City High School, rendered valuable assistance. The writer is most deeply indebted to Dr. T. C. Chamberlin and Prof. R. D. Salisbury, of the University of Chicago, for friendly interest shown while superintending the compiling of this manuscript. Professor Salisbury also personally directed a portion of the field work and made many practical suggestions. Thanks are also due Dr. G. K. Gilbert for careful criticism of the report. The area covered by this investigation lies along the eastern front of the Montana Rockies, between longitude 108° and 113° 40', and latitude 47° 15' and 49° 30'. Over the eastern and northern part of this area the ice from the northeast deposited its drift. Over the western part the ice from the Rockies pushed down the mountain valleys and, deploying on the plain, deposited large and well-defined terminal moraines. Extending from the Canadian line to the Missouri there is a strip of country, varying greatly in width, which the ice did not cover.