296 THE POPULAR SCIENCE MONTHLY, 



ice, the result is a layer of unassorted drift overlaid by a thickness of 

 handsomely-laminated fine clay and sand. This combination of cir- 

 cumstances must have occurred south of Lakes Erie and Huron, pro- 

 ducing the Black Swamp and the Cottonwood Swamp in Ohio and 

 Michigan, about the south end of Lake Michigan, and over an exten- 

 sive fiat south of the Winnipeg basin. 



All the phenomena of the drift in the Northwest are, heuce, at- 

 tributable to the approach, long duration, and slow disappearance of 

 the glacier-ice of Prof. L. Agassiz. It certainly seems unwarrantable 

 to propose upward and downward movements of the crust, involving 

 the submergence of the continent, when one simpler cause can be 

 shown sufficient to produce the known effects. The submergence of 

 the New-England coast to the depth of about seventy feet is all that 

 Prof. J. D. Dana finds warranted by a vigorous inspection of the drift- 

 deposits about New Haven, Connecticut. The four-hundred-foot 

 " beach," near Montreal, may have the same origin as the so-called 

 " beaches " that rise several hundred feet higher in the State of Ohio. 

 The Champlain and Terrace Epochs find no application to the drift in 

 the Northwest, as those terms are defined and used in the East. There 

 is abundant evidence throughout the West of a former higher stage 

 of the rivers. This higher stage may, however, be explained by re- 

 ferring it to the large increase of water incident to the melting of the 

 glacier only after reaching the latitude of a warmer climate. The ter- 

 races have not, moreover, in the Northwest, generally that system or 

 uniformity of height and arrangement necessary to warrant their ref- 

 erence to successive reductions in the volume of water, but are usually 

 due to a variable resistance offered by the banks or rocks in which 

 they occur, arising from their stratification. 



No well-authenticated fossil remains from the hard-pan drift have 

 yet been met with. Statements have been published of the finding of 

 fossil remains in the unmodified drift in various parts of the Northwest, 

 but they are generally based on the reports of non-scientific observers, 

 and must be taken with great caution, unless verified by a geologist 

 who has definite ideas of what " modified " or " unmodified " drift is. 

 It would not be improbable that, near the southern margin of the ice- 

 field, the remains of vegetation, and even of animals, should be in- 

 volved in the drift undergoing transportation, but their structures are 

 too fragile to withstand the grinding incident to the general progress 

 of the ice, and would not bear transportation from northern latitudes. 

 Much uncertainty is also thrown on the true age of vegetable remains 

 reported from the drift in the Northwest, by the wide-spread but hardly 

 distinguishable clays of the Tertiary and Cretaceous formations, which 

 contain modern species of wood and leaves, associated with marine 

 fossils. 



Believing, therefore, in the glacier origin, directly, of the Post-Ter- 

 tiary deposits of the Northwest, it is impossible to concur in the suppo- 



