132 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



known to be situated in the valleys of the Yellowstone, the Upper Mis- 

 souri, the Sun and Marias Rivers, the Gallatin, Madison, and Jefferson 

 Elvers, and the adjacent grassy plains or prairies bordering their tribu- 

 taries. All these levels lie below an altitude of 5,000 or 6,000 feet, and 

 usually not over 3,000 to 5,000 feet. 



The approximate area in which the locust permanently breeds lies 

 for the most part directly east of the true or main Rocky Mountain 

 Range, the breeding grounds west of the range being comparatively 

 limited. Perhaps one-fourth or one-tifth of the area lies in the lower 

 canons, parks (old lake basins), and valleys situated among the Rocky 

 Mountains. This area lies mainly between longitude 102° and 114^ 

 west of Greenwich and latitude 53° and 40^ north. 



Such, in general terms, are the limits of the native and permanent 

 breeding-grounds of this locust, and from which the destructive swarms 

 issue in comparatively slight numbers west and south, but in certain 

 years enormous quantities east, to ravage the States lying west of the 

 Mississippi River and east of the Great Plains. 



To enter more into detail, and beginning with that portion of British 

 America lying north of Montana, the Commission have no doubt but 

 that all the region lying south of the forest line and south of the 53d 

 parallel of latitude, including the lower half of the valley of the Korth 

 Saskatchewan as far north as Fort Pitt, is annually inhabited by the 

 Rocky Mountain locust. 



In the northwest, the limits do not quite reach Fore Edmonton. On 

 the west, the line follows the eastern flanks of the Rocky Mountains, 

 though it is possible that the western barrier above the 50th parallel of 

 latitude may be the Selkirk Mountains.^^ 



The eastern limits of the permanent breeding grounds we may set 

 down approximately as longitude 1040-105° west of Greenwich. The 

 region between this line and the Rocky Mountains is a treeless, elevated 

 plateau, rising gradually from an elevation of about 2,000 feet (Fort 

 Buford is 2,017 feet elevation) to 4,000 or 6,000 feet (Fort Shaw is 6,000 

 feet. Fort Ellis 4,747 feet, Helena 4,296 feet, Gallatm City 4,132 feet 

 elevation). It is possible that we have drawn the eastern limits of this 

 area too arbitrarily, and that it may follow the line of the Coteau of the 

 Missouri, at least within the limits of Dakota. The northern and eastern 

 limits of the plains are indicated on the map by the line indicating the 

 northern limits of the true prairie land, ^^ but there is reason to believe 



'8 North of the 49th parallel the Rocky Mountains are now known to extend to the Peace River, and 

 even farther northward, to near the mouth of the MacKenzie, and to maintain throughout much the 

 same geological character with that of their southern portion. The Purcell, Selkirk, Columbia, Cari- 

 boo, and farther north the Omineca Mountains may be taken collectively as the representatives of the 

 Bitter Root Ranges of Idaho. The interior plateau of British Columbia represents the great basin of 

 Utah and Nevada, but north of the southern sources of the Columbia this region is not self-contained 

 as to its drainage, but discharges its waters to the Pacific. — [G. M. Dawson's general note on the mines 

 and minends of economic value of British Columbia, Geological Survey of Cauada, 1877.] 



*9This and the southern limits of the tiue forests are taken from dati published in Palliser's map, and 

 reproduced in a map of the country to be traversed by the Canadian Pacific Railway. — [Sanford Flem- 

 ing, engineer iu chief, 1876.] 



