382 PLEISTOCENE OF INDIANA AND MICHIGAN. 



DISTINGUISHING CHARACTERISTICS. 



In general the Whittlesey beach is remarkable for the height to which it is built above the 

 plain in front of it and for the boldness of its slope both in front and rear. It is generally com- 

 posed of gravel, with a rather large proportion of sand, and everywhere, excepting in connection 

 with certain delta deriosits, it is remarkable for the singleness of its form, in many places the 

 steepness of the beach in front along its base suggests the idea that it has been slightly undercut 

 by wave action since it was made, but no other evidence of such undercutting was found. If 

 such had occurred it would be expected to produce constructive forms in some localities, but 

 nothing of this kind has been observed except beach A (see p. 369), which is probably of dif- 

 ferent origin. 



The manner in which Lake Whittlesey came into existence (by readvance of the ice and 

 raising of the water level) explains certain characters which mark this beach more strongly than 

 any other that has been found. Its course across the country is remarkably direct in view of its 

 many crossings of river and creek valleys, which appear to have been excavated to approxi- 

 mately their present depths before this beach was made. It crosses these in a direct line, like 

 a railroad embankment, in places standing 20 to 25 feet above the valley floor at its back. 



It is significant, in the first place, that the river and creek valleys were eroded out to such 

 an extent before this beach was made. This shows clearly that the lake level and consequently 

 the base-level of erosion were for a considerable time lower than Lake Whittlesey before 

 that lake came into existence. This would naturally have been the case during the time of 

 Lake Arkona, for the streams during all the period of that lake at its different stages were cutting 

 down to it as a base-level. When Lake Whittlesey was subsequently raised to a higher level, 

 it found these stream valleys already carved apparently to nearly their present proportions. 



Some other beaches show clear evidence of weak or short-lived wave action at the back of 

 bays or reentrants of their shores which were subsequently cut off by spits or bars built at the 

 same stage of the lake. Such a relation indicates that the faint beach at the back of the bay 

 was built before the shore currents had projected the spit across the front of the depression. 



This, however, is not the case with the Whittlesey beach at any locality observed. Not 

 the slightest evidence of wave action appears at its level in embayments at its rear. This fact 

 and its extraordinary height and boldness suggest that it was built rapidly and was pushed a 

 few feet up the slope while it was being built, so that the back shore of the bays closed by 

 barriers was never exposed to wave action at the level at which the beach was made. 



The supply of material for building the ridge seems to have been uncommonly plentiful 

 and easy of access by the storm waves. This, again, would naturally be true for Lake Whittlesey, 

 because the greater bulk of the gravel in the Arkona ridges was torn away and swept up the 

 slope by the storm waves. Such conditions would be especially favorable for the production 

 of just such characters as are found in the Whittlesey beach. 



The head of the outlet of Lake Whittlesey is a broad flat with two openings across a low 

 divide. The one at Tyre is floored with nearly horizontal beds of sandstone. It seems quite 

 likely that as the moraine pushed up the slope from the north the outlet had this sandstone 

 for its sill for some time before the final halt of the advancing ice. If that were true it is easy 

 to see how the level of the lake was gradually raised in the last stages of advance and the beach 

 pushed a few feet up the slope. This may be true, although it seems also true that the first 

 raising of the waters when the ice began to advance was relatively rapid. It appears at least 

 to have been sufficiently rapid for the Arkona beach ridges a mile northeast of Spring Hill to 

 have escaped modification in any perceptible degree by the waves, which would certainly not 

 have been the case if the lake level had rested for any length of time in such a position that 

 the surf would strike them. The truth of this statement does not in any way conflict with 

 the conclusion previously stated that the storm waves running up the Black Kiver valley 

 lengthwise of the Arkona ridges apparently had no effect in modifying them, for this was 

 when the beaches were submerged to a considerable depth and not exposed to the direct action 

 of the surf. 



