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THE POPULAR SCIENCE MONTHLY, 



Tizcapa, which furnished the material form- 

 ing the tufas on which the foot-prints occur, 

 is one of several in the vicinity which have 

 long been extinct, and whose craters are oc- 

 cupied by deep and still lakes. Dr. Brinton's 

 specimen was taken from a quarry on the 

 lake-shore at a point where the overlying 

 strata present a thickness of twenty-one feet 

 beneath the surface soil. These strata com- 

 prise five well-marked beds of tufa, beneath 

 which is a deposit of clay, and below this 

 four more beds, with other accumulations in 

 the scams, of pumice and volcanic sand. A 

 heavy deposit of tufa, lying on yellow sand, 

 is then reached. This is the last in the se- 

 ries, and bears on its upper surface innu- 

 merable foot-prints — some deeply imprinted, 

 while others are but superficial impressions. 

 As to the age of the foot-prints. Dr. Flint 

 believes the yellow sand under them to be 

 Eocene, but the small shells which it con- 

 tains are deemed by Prof. Angelo Heilprin 

 to be more nearly Post-pliocene than Eocene. 

 In view of this, and the indications furnished 

 by the overlying strata, Dr. Brinton concludes 

 that there is not sufficient evidence to re- 

 move the foot-prints further back than the 

 present Post-pliocene or Quaternary period. 



The Lake-Age in Ohio.— Prof. E. W. 



Claypole has investigated the series of events 

 that occurred in Ohio and the adjoining region 

 during the final retreat of the North Amer- 

 ican glacier, and has thrown into one view 

 what is known of these occurrences. The 

 terminal moraine of the great glacier crosses 

 the eastern boundary of Ohio a little north 

 of the Ohio River, and extends west and 

 southwest, crossing the Ohio River near Cin- 

 cinnati. The ice here dammed the river, and 

 ponded back its waters for hundreds of miles. 

 The banks of the Ohio at Cincinnati rise from 

 four hundred to five hundred feet above the 

 water; hence, in order that the ice may have 

 been high enough to pass over into Kentucky, 

 it must have had in the bed of the river a 

 thickness of five hundred to six hundred 

 feet. In this way was formed a lake, which 

 Prof. Claypole calls Lake Ohio, occupying a 

 large tract of the low lands on both sides of 

 the main stream and its tributaries, extend- 

 ing on the north to the edge of the ice-sheet, 

 and hence covering a large share of the 

 southern and eastern parts of the State, i-each- 



ing beyond the site of Pittsburgh, with arms 

 running up the valleys of the Alleghany and 

 Monongahela Rivers. Lake Ohio must have 

 had a length of four hundred miles, measured 

 in a straight line, and a width of two hun- 

 dred. Its outlet was probably near Cincin- 

 nati, and followed the valleys of the Licking 

 and Kentucky Rivers to that of the Ohio 

 below the ice-dam. When the amelioration 

 of the climate caused the great glacier to 

 retreat northward, there must have come a 

 time when the dam had melted down so that 

 the water could flow over it. A channel was 

 quickly cut in the ice, and the foundations 

 of the dam were undermined. Finally, the 

 dam broke, and all the accumulated water of 

 Lake Ohio was poured through the gap. 

 Days or even weeks must have passed before 

 it was all gone, but at last the lake-bed was 

 dry. When the ice-sheet had been pushed 

 back north of the water-shed which separates 

 the streams that flow into Lake Erie from 

 those that flow into the Ohio River, the water 

 that came from the melting of the ice was 

 held between the front of the retreating ice 

 and the ridge of the land. Thus in the 

 valleys of the Cuyahoga, Sandusky, Maumee, 

 and other north-flowing rivers, triangular 

 lakes were formed with their bases rest- 

 ing against the ice-wall, and narrowing and 

 shallowing back to the water-shed, where 

 they found outlets in south-flowing rivers. 

 All these lakes left monuments behind them 

 in the form of beds of silt, in which are im- 

 bedded stones such as might be dropped by 

 floating masses of ice. As the ice-line shrank 

 back down the slope toward Lake Erie, the 

 bases of these triangular lakes spread until 

 they came in communication with each other, 

 and the chain formed one continuous lake, 

 using the lowest of the several southern out- 

 lets which had belonged to the separate lakes. 

 As the bed of Lake Erie became uncovered 

 by the glacier, this ancient lake increased in 

 extent, and there is evidence which indicates 

 that when the ice-sheet had retreated still 

 fai-ther the lake formed one vast sheet of 

 water occupying the beds of Lakes Erie and 

 Ontario, the southern part of the bed of 

 Lake Huron, and much of the surrounding 

 country. There was no escape for this water 

 through the St. Lawrence River ; that pas- 

 age was still blocked by the ice. Where 

 Fort Wayne, Ind., now stands, there is a gap 



