644 REPORT UNITED STATES GEOLOGICAL SURVEY. 



with some certainty be predicted, and, again, its arrival in Kansas and 

 adjoining States be announced with a certain amount of precision, as 

 has already been done by Dr. Riley, but we shall be able to foretell the 

 course taken in the return tiight of their progeny in the succeeding 

 year. I will confess that previous to my visit to Kansas and Colorado, 

 in 1875, I was skeptical as to Dr. Riley's opinion that there was a gen- 

 eral movement in a northwest course of the young of the previous year, 

 broods from Missouri and adjoining regions northwestward. The facts 

 and resulting theory'' have already been stated in full by Dr. Riley and 

 others. It remains to determine the causes of this return migration, this 

 completion of the " migration-cycle," as Professor Dawson terms it. 

 It is evident that in this case the desire for food is not the cause, for food 

 is many times more abundant in the Mississippi Valley than on the 

 plains whither they return. The solution of the problem, I think, must 

 be sought in the direction of the prevailing winds during the miildle of 

 June, tlie time when they become winged. It may be found, after a 

 series of careful meteorological observations, that the prevailing winds 

 at this early season are southerly and southeasterly. It has been shown 

 by nieteorologists, as I learn from Prof. C. Abbe, that during May and 

 June the winds blow inward toward the heart of the continent from the 

 Atlantic Ocean and Gulf of Mexico. On application to General A. J. 

 Myer, Chief of the Signal-Service of the United States Ar:uy, for the 

 meteorological data necessary to confirm this hypothesis, I promptly 

 received a full summary of data observed by the officers of the Weather 

 Signal Bureau, for periods of from two to live (usually the latter) years 

 between 1871 and 1876, ivhich show that the prevailing winds in June, 

 in Davenport, Dodge City, and Keokuk, Iowa ; Saint Paul and Breck- 

 enridge, Minn.; Yankton and Fort Sully, Dak.; Omaha, Leavenworth, 

 and Fort Gibson, Ind. T. — all within the lotnistarea — are from thesouth- 

 east and south. This fact may be sutjficient to account for the prevail- 

 ing course of the return migrations of the locust from the eastern limits 

 of the locust area. 



The accompanying table is taken from a synopsis of the meteorological 

 phenomena of the Western States and Territories within the eastern 

 limits of the locust area, which is appended to this chapter. It has 

 been furnished me by Bi ig. Gen. A. J. Myer, U. S. A., Chief Sigual- 

 Officer, Washington, D. C, and my he.irty thanks are due him for the 

 labor and trouble involved in its preparaiion. 



