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THE POPULAR SCIENCE MONTHLY. 



might have existed during a very long time, 

 instead of for a few weeks, as happens af- 

 ter a modern winter. Again, the slackened 

 or suspended flow of the water, caused by 

 such ice-obstructions, would have favored 

 the deposition and accumulation about them 

 of drift, and some may have thus been con- 

 verted into complete dams. This process 

 might occasionally have wholly filled with 

 earthy material a gorge or narrow valley 

 as in the Niagara River so as to block up 

 and divert the course of the stream. 



Iu view of these probable conditions of 

 the river-valleys during the glacial flood, the 

 question arises whether the height of the 

 upper terraces above the narrows, on the 

 rivers of Connecticut, was not partly owing 

 to the existence of ice-obstructions. That 

 this was so seems highly probable ; and the 

 height of modern spring-floods in the Con- 

 necticut at Middletown and Hartford is now 

 often due, in part, to this very cause. If 

 such obstructions existed in the Thames, 

 Connecticut, and Housatonic Valleys, they 

 were only partial obstructions, for in the 

 case of each the terrace of the valley below 

 the narrows declines quite gradually in height 

 from the level above the narrows, instead 

 of abruptly. Moreover, the material of the 

 terraces below the narrows is like that 

 above. Further evidence of the existence 

 of such ice-barriers is to be looked for in a 

 distribution of gravel and large bowlders 

 across the valley just above the narrows, 

 where the ice-masses had been brought to a 

 stop and piled up. Prof. Dana has as yet 

 observed no satisfactory evidence of this 

 kind, but thinks the question needs more 

 investigation. 



Where the Army-Worm Moth lays its 



Eggs. The mode of oviposition in Leucania 

 unipuncta (the army-worm moth) was, till 

 the other day, an unsolved problem in ento- 

 mology. During the current year Prof. C. 

 V. Riley, State Entomologist of Missouri, 

 undertook the methodical investigation of 

 this subject, and at the meeting of the St. 

 Louis Academy of Science, on May 1st, was 

 able to announce that his researches had 

 been entirely successful. Guided by the 

 structure of the ovipositor, Mr. Riley con- 

 cluded that the moth would naturally secrete 

 the eggs where they could not be easily 



seen. This conclusion was afterward veri- 

 fied bv direct observation, the author having 

 witnessed the mode of oviposition on blue 

 grass. The eggs are, as he surmised, se- 

 creted, being either glued in rows of from 

 five to twenty in the groove which is formed 

 by the folding of the terminal grass-blade, 

 or else between the sheath and the stalk. 

 The eggs are white, slightly iridescent, 

 spherical, .02 inch in diameter. They are 

 fastened to each other and to the leaf, and 

 covered along the exposed portion by a 

 white, glistening, viscid substance. As they 

 mature the color becomes yellowish, and by 

 the seventh day the brown head of the em- 

 bryo shows distinctly through the shell. 

 The larva emerges from the eighth to the 

 tenth day, is 1.7 millimetre in length, dull, 

 translucent white in color, with a large 

 black-brown head, and is a looper, the two 

 front pairs of abdominal prolegs being at- 

 rophied. On account of its extremely small 

 size and of the color resembling the pale 

 bases of the grass-stalks near the ground, 

 it is almost impossible to find them even 

 where they are numerous. The one great 

 economical result of these researches is the 

 indicating of an effectual mode of destroy- 

 ing the army-worm viz., burning the eggs 

 with the stubble. 



How the Mississippi wears away its Banks. 



The observation is made by Rcclus, in his 

 work "The Earth," that the Mississippi 

 River seems to contradict the law of dis- 

 placement of running water, which in con- 

 sequence of the motion of the earth on its 

 axis causes all streams which flow north or 

 south to hug the west side of their valleys. 

 But Mr. G. W. R. Bailey, in a paper pub- 

 lished in the Journal of the American Socie- 

 ty of Civil Engineers, shows that the anoma- 

 ly is an apparent one only. " The river," he 

 writes, " does wear away its western shore- 

 line more rapidly than the eastern, but it 

 cannot do otherwise than gradually excavate 

 circular bends, of from twenty to twenty- 

 five miles in circumference generally, and 

 then cut them off, leaving them to the west- 

 ward. There has been, always, an excess 

 of overflow and of sedimentary deposits 

 west, and by far the largest number, as well 

 as the greatest bends when cut off, have 

 been left to the west. The western portion 



