4 THE GEOLOGY OP MINNESOTA. 



[Conglomeratic jaspilyte. 



On the portage trail from Moose lake to Wood (or Wind) lake, but near Moose 

 lake, and near the section line between sees. 20 and 21, T. 64-9, is a very interesting 

 locality. The country, at the time visited, had recently been burnt over and the 

 rock was bare, showing its structure. There is a series of east-northeast and west- 

 southwest ridges crossing the country parallel to the direction of the lake and of the 

 islands, and on the portage trail they are quite conspicuous. At the lake is schist, 

 quite fissile, as seen on some of the islands and the points, and argillyte, often green 

 and falling down in large slabs, probably suitable for roofing slate. Immediately 

 north of the portage landing rises a very singular and interesting ridge, which is 

 steep on the south side and slants with the dip, and is somewhat more gradual on 

 the north. The dip is 80 or 85 to the south. 



This ridge is made up of conglomerate, in general terms, but shows interesting 

 combinations. 



1. It contains considerable deposits of jaspilyte, normal in all essential char- 

 acters, rather magnetitic than hematitic, but considerably contorted and varying to 

 a greenish siliceous jaspilyte and to dark slate. 



2. This jaspilyte embraces rocks of different kinds as pebbles, and even occa- 

 sionally as boulders, and the jaspilyte banding swings round and embraces them 

 when large. The enclosed stones are of different sorts, but red granitic rock prevails. 

 Such red granite boulders are also the prevalent pebble throughout that portion of 

 this great conglomerate. Greenstone pebbles, hard, siliceous, greenish pebbles, and 

 apparently pebbles of jaspilyte that is fiery red in color, are also included in the 

 jaspilyte, yet, in the main, it is simply a banded jasper, nearly free from pebbles. 

 Of one red granite boulder, about ten inches in diameter, a photograph was made 

 (plate X, vol. iv). The jaspilyte is indigenous in the formation and its layers are 

 frequently separated by fine green sediment, and sometimes by a coarser gritty green 

 sediment. When the interleaved green sediment is fine and greenish it is sometimes 

 also very siliceous, making a green flint. It is necessary to infer that the origin of 

 the jaspilyte with its irony ingredient was cotemporary with a fragmental accumu- 

 lation, the two processes operating simultaneously at the same point. No known 

 agent is capable of such double process except oceanic water from which were being 

 precipitated both iron and silica. 



3. The conglomerate in its southern portion is characterized by a red weather- 

 ing granite, but it also contains greenstone and jaspilyte and a siliceous, very fine 

 rock like flint. 



4. The jaspilyte itself occurs not only as large masses, but is strung out 

 in small, lenticular, thin sheets, throughout the southern part of this conglomerate, 

 and it fades out sometimes across the bedding into the general conglomerate, passing 

 through a stage of siliceous, black or greenish slate. 



