319 



Some interesting facts in relation to the assumption, tliat tlie waters 

 of the great lakes were formerly at a much higher level than at present, 

 covering a large part of the border portions of the Peninsula, were no- 

 ticed in my report of last year. During the past season, a continuation 

 of the " ridge," which is supposed to coincide with the beach of the 

 ancient lake, has been traced through Macomb into St. Clair county ; 

 and further facts, confirmatory of the positions assumed last year, were 

 observed in other more northerly districts. In the county of Macomb, 

 this ridge has been much broken up by crossing streams, and is very ir- 

 regular, showing frequently the existence of large entering bays and cur- 

 vatures of the coast. This was the more particularly noticed, from the 

 fact that elsewhere, so far as observed, the course of the ridge is very 

 remarkably continuous and well defined. In this county, also, a num- 

 ber of inferior ridges of evidently similar origin, were observed, between 

 the main one and the present lake shore ; leading to the supposition, 

 that the subsidence of the waters did not take place gradually and con- 

 stantly, but that sudden lapses occurred, and the water line had been 

 stationary at intervals. 



The soil and detrital matter superficially covering that portion of the 

 Peninsula which is embraced between this ancient lake ridge and the 

 present shore of the lakes, I have denominated ancient alluvion, to dis- 

 tinguish them, as well from alluvions now in process of formation, as 

 from the immense mass of diluviums which overepread the whole inte- 

 rior of the State, beyond this separating ridge. 



The portion thus distinguished by alluvial deposits, embraces a broad 

 belt of border country, varying in width from about 25 to 50 miles. 

 It is, with small local exceptions, heavily timbered and very level. But, 

 on passing the bounding ridge, there is in general, an almost immediate 

 change to a soil of coarser chai-acter, and a more undulating surface. 

 This ancient alluvion is a deposit, from a quiescent condition of the 

 waters, and similar to that which is now taking place in the beds of the 

 present lakes. It forms in general, but a thin mantle to the underlying 

 formations, consisting often of mere ridges of sand, and owing to the 

 deprivation of its lime, has, in general, less fertility than the diluviums. 



The heavily timbered district is not altogether coincident with the 

 extent of this alluvion, but is dependent chiefly upon the following 

 cause : Throughout their whole extent, the alluvions are underlaid by 



