258 ANNUAL OF SCIENTIFIC DISCOVERY. 



which four hundred species were already known. In comparing the 

 proportion of new species from the northern and north-western locali- 

 ties, there were scarcely more than ten per cent, of new species, while, 

 at the same distance to the south-west, the proportion was ten times as 

 great. Whether or not this proportion would hold true on further 

 examination, it could not now be determined, but since so many speci- 

 mens had been collected, and over such wide areas, it was evident that 

 there were most incontestable proofs of the occurrence of a larger num- 

 ber of species in localities at the south than in northern localities 

 of the same extent. This difference was, therefore, to be accounted for 

 either from climatic agencies, or from other circumstances more favor- 

 able to the development of species in the southern than in the uorth- 

 ren localities. 



REPORT ON THE GEOLOGY OF THE LAKE SUPERIOR LAND DISTRICT. 



THE first report of Messrs. Foster and Whitney, United States Geolo- 

 gists, for the Lake Superior Land District, has been published during 

 the past year. It forms a volume of 224 pages, illustrated by numer- 

 ous charts, maps and plates. From its pages we take the following 

 notes : 



The Lake Superior Land District is bounded on the north by Lake 

 Superior, east by St. Mary's river, south by Lakes Huron and Michi- 

 gan, and west by the Montreal and Menomonee rivers, being situated 

 between 45 and 49 north latitude and 83 45' and 90 33' west longi- 

 tude. A striking feature in the topography of the region is the paral- 

 lelism of the north-west shore of Lake Superior, the south shore, west 

 of Keweenaw Point, and the narrow island of Isle Royal between, 

 proving, as the authors state, that this part of the lake must be the 

 course of a great synclinal valley, arising from two parallel axes of 

 elevation on opposite sides of the lake. We might add, farther, that 

 this course is at right angles to the great range of lakes that extends 

 from Erie and Michigan north-west to the Northern ocean, which range 

 is parallel to the Rocky Mountains and the north-west coast of America 

 on one side, and to Hudson's Bay and the shores of Davis 'Straits on 

 the other. The district contains an area of 16,237 square miles. 

 The number of rivers comprised in it is 34, of which the largest is 

 the Menomonee. Their aggregate length is 1,478 miles, and the area 

 drained is 10,530 square miles. The course of the rivers is chiefly 

 north-west, the outlets of eighteen being in Lake Superior. The re- 

 mainder fall into Lake Michigan, Keweenaw Bay, or Lake Huron, or 

 are tributaries of the larger rivers. 



The mountains of the region consist of two granite belts in the 

 north-west, the Huron Mountains to the southward, a trap range start- 

 ing from the head of Keweenaw Point and running west and south- 

 west into Wisconsin, and the Porcupine Mountains. The Huron 

 Moun tains in places attain an elevation of 1,200 feet above the lake. 

 The highest elevation attained by the Porcupine Mountains is 1,380 feet. 



Meteorological observations were instituted, by order of the govern- 

 ment, at three military posts in the district, viz., Forts Wilkins, Brady 



