NIPISSING GREAT LAKES. 449 



through this outlet the expanse of the waters in the basin of the modern Lake Nipissing was very 

 little greater than it is now and was much too small for the generation of powerful waves like 

 those of the Great Lakes. The strong beach in this basin is therefore an indication that wave 

 action lasted for a considerable time. Account must also be taken of the great strength of the 

 Nipissing beach near the isobase of North Bay on the north shore of Lake Superior, which seems 

 to indicate that the water plane of the Nipissing Lakes lasted considerably longer than that of 

 the succeeding transitional two-outlet stage. 



In the early part of this closing two-outlet stage a very small discharge probably went by 

 way of Illinois River at Chicago, for the col there is only 8 feet and the Nipissing beach about 15 

 feet above the modern lake. The latter measurement, however, is the top of the beach ridge, 

 and the water surface was probably 3 or 4 feet lower. This small discharge at Chicago ceased 

 as soon as the outlet at Port Huron had cut down 3 or 4 feet. 



NIPISSING BEACH. 



The name "Nipissing beach" has from the first been applied to the shore line now known 

 to have been formed during the two-outlet stage of the lakes, when the discharge was deserting 

 North Bay and returning to Port Huron and the Nipissing Great Lakes were coming to an 

 end. This shore line is therefore, in reality, the beach of a transition stage, but it is so strongly 

 developed and is so prominent around all the shores of the upper lakes that it has become firmly 

 known as the Nipissing beach, in spite of the fact that this name properly belongs to the slightly 

 older beach made by the Nipissing Great Lakes when their whole discharge passed eastward to 

 Ottawa River. 



After the formation of the true Nipissing beach the whole region was differentially elevated, 

 depressing the water plane to the north and raising it to the south of the isobase of the North 

 Bay outlet. This isobase runs about west-northwest, and only a little of the Lake Superior of 

 that time lay north of it. The whole area of the Nipissing Great Lakes south of this line was 

 flooded by the backing up of the water, and the original Nipissing beach and its successors, up 

 to the time when the Port Huron outlet equally divided the flow with the North Bay outlet, 

 were submerged and probably to a large degree destroyed. Hence the original Nipissing beach 

 in unmodified form is to be seen, if anywhere, only in a small area in the northeast corner of 

 Lake Superior, and it seems easier to qualify the name of that beach by calling it the "first" 

 or " original" Nipissing beach than to try to change the name by which the beach of the transition 

 or two-outlet stage has come to be known. Accordingly, the established usage is followed here. 



DISCRIMINATION FROM ALGONQUIN BEACHES. 



The differential elevation which affected the Nipissing beach appears to have hinged on 

 the same fine as that which affected the highest Algonquin beach. 1 South of this fine, therefore, 

 in the basins of Lakes Huron and Michigan lies the area of horizontality, so far as relates to 

 this beach. Within this area in both basins measurements of the altitude of the Nipissing 

 beach vary between 14 and 16 feet above present lake level, the mean being in general about 

 15 feet. 



In the area of horizontality the relation of this beach to the Algonquin shore fine is such 

 that for short distances in many places it is impossible to distinguish the two. Both lie in 

 horizontal planes, the Nipissing being 10 to 12 feet below the Algonquin. Where the Algon- 

 quin is represented by several strong ridges descending by short steps toward the lake, the 

 Nipissing beach may appear as one of these ridges without any distinguishing characteristics. 



This relation, however, obtains for only relatively short distances. Within a mile or 

 two from nearly all such places some distinguishing characteristic or evidence of discordance 



1 This relation seems clearly established in the basin of Lake Michigan, but owing to the difficulty of determining the Nipissing beach, it remains 

 somewhat uncertain in the basin of Lake Huron. In the basin of Lake Superior the two hinge lines may be separated by a considerable 

 interval. 



