MICHIGAN ACADEMY OF SCIENCE. 141" 



of Gratiot and Montcalm and thence northwestward towards Manistee and 

 Ludington where the former drainage was not far from sea level, there being 

 a droj) of not less than 400 feet in its course westward from Saginaw Bay. 

 1 A\'ouI{l suggest the name of Alma channel for this former drainage course 

 as the upper reaches of this channel passes vuiderneath that town where 

 the depth has been obtained. It will be observed that this former drainage 

 channel is more or less parallel and just north of the present Saginaw-Maple 

 river valley, and a portion of the Grand river to which the Maple is tributary. 

 It seems not impossible that the very large amount of glacial debris which 

 would be reciuired to fill the former Alma chaimel resulted in a lack of ma- 

 terial further south, the result being the depression forming the present 

 area of the Saginaw-Maple-Grand valley, across which a shiji canal was at 

 one time projected. The present depressed topographic feature was also 

 very likely considerably lowered during the lacustrine period toward the 

 close of the Pleistocene, when the drainage of a portion of the former glacial 

 lake series had an outlet near Pewamo and thence drained westward into 

 the basin of the Grand river. In Bay county we have coming into this Alma 

 channel the Beaver, Auburn, Amelith and Souwestconning channels, all the 

 drainage being westward and south west ward. They have there been desig- 

 nated washouts in deference to the usage among the miners, which is more- 

 over appropriate and perhaps worthy of continuance, but on the other hand 

 it is well to have all the unity compatable with scientific accuracy. Within 

 the 400-foot above tide rock contour line the Alma channel has an area of 

 about 2,751 square miles and an average depth of 162 feet. To this, how- 

 ever, should perhaps be added a depth of 300 feet for erosion during the 

 glacial period, which figure represents the possible average depth of glacial 

 and glacio-fluvial deposits and therefore since a greater part of the glacial 

 drift, soils and subsoils, was probably only carried a comparatively 

 short distance, the amount of erosion in the peneplain through which the 

 Alma channel worked its way. Conseciuently we have an average depth of 

 462 feet if not more for this buried channel in its theoretical restoration. 

 This does not, however, take into account a certain amount of erosion of 

 the Alma basin during Mesozoic and Cenozoic times, beyond the limits of 

 the apparent valley, and I do not know of any way in which this amount 

 of erosion can be determined. Since very nearly all streams have their outlets 

 either into lakes, gulfs, seas or oceans, it is necessary to infer that the Alma 

 channel either emptied its burden of sediment into a former lake in the area 

 occupied by at least a portion of the present body of Lake Michigan, or on 

 the other hand the channel may have been continued onward. Since stream 

 development is both progressively downward in cutting its channel, and also 

 away froni its outlet- by head erosion it is necessary to add to the approxi- 

 mate vertical depth near its apparent outlet above Ludington, a later de- 

 velopment of this same chaimel as in its upper reaches near Bay county 

 As near as I can calculate this would give an erosive record of some 400 feet 

 to which will be added 300 feet of erosion as represented by the record oblite- 

 rated during the glacial period. This entire estimate is at least a portion of 

 the erosion which took place during Mesozoic and Cenozoic times. This com- 

 bined record, therefore, may represent a vertical ec|uivalent of 700 feet. 



