The Kezv£e?iaioan in Minnesota. — Elfttnan. 185 
Tlie Temperanec Riz'er ;/ieuiber. Between this and the 
preceding members is a considerable unconformity. The 
older members were extensively eroded. In places a con- 
glomerate and quartzyte over one hundred feet in thickness 
form the basal strata. Upon the quartzyte and contemporan- 
eous with part of it are found basic and intermediate surface 
Hows. The flows which followed consist of diabase and dia- 
base porphyryte, with a strong development of amygdaloidal 
structure in the upper part of each flow. Numerous inter- 
bedded layers of sandstone, sometimes 250 feet thick, though 
usually from a few inches to a few feet, are found in all parts 
of the member. In certain parts of the older members are 
found several areas of basic intrusive rocks varying in struc- 
ture from that of a gabbro to that of a diabase. These are 
tentatively correlated with this member, and may probably 
represent fissures or vents through which the surface flows 
were ejected. The land was submerged, and it is noticeable 
that the volcanic activity decreased and the deposition of sedi- 
mentary rocks increased toward the top of the formation. This 
member includes the greater part of the Agate Bay, the east- 
ern end of the Duluth and all of the Temperance River groups 
of Irving. The unconformit}' at the base of the Temperance 
River member, in places, has been identified by Prof. N. H. 
Winchell as the division line between the Norian and the 
Keweenawan. From the descriptions of these divisions, as 
given by Prof. Winchell, it is evident that part of his Norian 
belongs above and part of his Keweenawan belongs below this 
luiconformity. 
The Later Diabase nientber. A large number of diabase 
dikes and sills are found cutting all of the preceding members. 
The areal distribution of these is comparatively small. Since 
they are later than all of the rest of the Keweenawan at pres- 
ent found in this region, they are thrown into a separate mem- 
ber. These dikes may not all be of the same age. In this 
member are included rocks w^iich are found in all of Irving's 
grou])s, especially the Duluth group south of lirule lake. 
The "black rock" of Winchell forms a ])n)mineiU feature of 
the group. This group occurs at numerous places along 
lake Superior coast antl frequently is indistinguishable from 
tlie black (lial)ases which it cuts. 
