PLATE LXXXIV. 



MOUNTAIN LAKE PLATE, 1899. U. S. GEANT. 



On the international boundary a drift-covered tract begins about two miles south 

 of South Fowl lake and extends to the eastern limit of this plate, and to the north- 

 west end of the "Grand Portage" trail, on the next plate, being at least four miles 

 wide. This drifted belt runs westward to the region of East Greenwood lake, and 

 probably much further, but its direction and its features have not been ascertained, 

 though it certainly passes south of the Misquah hills. Mr. Elftman has mapped it 

 in a provisional manner as running southwestwardly to Devil's Track lake, north of 

 Grand Marais,* forming a moraine of the Lake Superior ice-lobe, his Highland moraine. 

 A part of this tract, on the international boundary, is flat and covered with lacustrine 

 clay, making a very good agricultural area. It is certain, therefore, that the waters 

 of the Pigeon river were dammed by the ice, forming a glacial lake. This has been 

 named lake Omimi by Mr. Elftman. 



The topography which is formed by the rocks proper undergoes a change in 

 the area of this plate. The features of the Animikie province pass into Canada at 

 the north side of this drift-covered belt, and the igneous rock that constitutes the 

 sills in the Animikie proper appears in the form of dikes along the south of that belt. 

 This feature only begins in this area, but is fully developed in the Pigeon Point plate 

 area. These dikes are sometimes over a hundred feet wide, and rise boldly above the 

 general surface, and do not have as much uniformity of direction as in the plates 

 further west. 



The rock which these dikes pass through is different from the Animikie that is 

 characterized by sills of igneous rock. It is a kind of greenish graywacke, more 

 fragile than the Animikie quartzytes and slates and not rigidly bedded, comprising 

 much igneous matter. It has been named Grand Portage graywacke, from its geo- 

 graphic position. It has been supposed to be a part of the Animikie (the uppermost 

 part), but it seems to run below not only the Puckwunge conglomerate but also the 

 quartzytes and slates at Grand Portage village and of Pigeon point, which have been 

 classed as Animikie, since the overlying conglomerate (the Puckwunge) seen in Grand 

 Portage island contains their debris. As a formation this greenish-gray graywacke 

 is not well known. 



The Puckwunge conglomerate is taken to be the sedimentary base of the upper 

 part of the Keweenawan. It is included in the Potsdam. The trap beds which overlie 

 it are in the Manitou igneous epoch of the Keweenewan. N. H. w. 



"A mrrimn Gcolvyixt, vol. .\xi, plate XI. February, 1898. 



