Davis.] 58 [May 3, 



will also change. The argument from the amount of drift is es- 

 pecially open to correction in this respect. But when all allow- 

 ance is made for these chances of error, it is believed that the 

 several lines of argument point with substantial agreement to 

 the following results. 



Summary. The amount of glacial erosion in the central dis- 

 tricts has been very considerable, but not greatly in excess of pre- 

 glacial soils and old talus and alluvial deposits. Most of the 

 solid rock that was carried away came from ledges rather than 

 from valleys ; and glaciers had in general a smoothing rather than 

 a roughening effect. In the outer areas on which the ice ad- 

 vanced it only rubbed down the projecting points ; here it acted 

 more frequently as a depositing than as an eroding agent. 



No large lakes have been produced by glacial erosion: the 

 number of true rock-basins of erosion has been greatly exagger- 

 ated. The most considerable topographic effect produced by 

 glaciers is the heaping of various morainal deposits on an area 

 smaller than their source, and in this way very often forming hills 

 of considerable size. A similar indirect result of glacial erosion 

 is seen in the very numerous lakes made by drift obstructions in 

 preglacial valleys. 



The following paper was also presented : 



OLDER FOSSIL INSECTS WEST OF THE MISSISSIPPI. 



BY SAMUEL H. SCUDDER. 



Mr. R. D. Lacoe, to whom I am so largely indebted for mate- 

 rial in studying carboniferous insects, has recently sent me from 

 Kansas City, Missouri, a specimen (No. 2030) of an heteropterous 

 Hemipteron found in beds claimed to be carboniferous, and which, 

 according to the Missouri geological reports, have eight hun- 

 dred feet of coal measures above them. It consists of an ex- 

 cellently preserved front wing, showing clearly the venation, 

 with the division of the wing into distinct areas as well marked 

 as in modern types. The corium is extensive, as in the modern 

 genus Zaitha, and the membrane covered with faint arborescent 



