184 The American Geologist. March, i8st6 
with the JJeaver Bay diabase. The member consists chiefly of 
the massive flows of coarse diabase which inclose the anor- 
thosytes of the Minnesota coast. Above these are numerous 
thinner flows of diabase, diabase porphyryte and amygda- 
loidal dial)ase. In the upper part of the member are thin lay- 
ers or patches of volcanic ash. It is evident that this member 
consists of basic surface flows with more or less volcanic frag- 
mental rocks. The rocks as exposed above lake Superior 
show that during the accumulation of this member the sur- 
face was not submerged beneath the ocean. The fragmental 
rocks point toward a formation upon an exposed surface. The 
position of this member in the series is such that it may be 
regarded as contemporary with the gabbro. Iioth consist of 
basic rocks; the one is intrusive and the other effusive. These 
and other facts indicate that the Gabbro and Beaver Bay 
Diabase menfl:)ers are complementary parts of one eruptive 
epoch. In the present paper the two are considered as two 
members in order to establish the individual characters of 
each. When this is done a further correlation may be at- 
tempted. The rocks included in this member include part of 
the Duluth, Lester River, Agate Bay and Beaver Bay groups 
of Irving. The name Beaver Bay Diabase is given to the 
member because all of the essential characters appear in the 
region of which Beaver Bay forms the central point. This 
diabase also forms the greater part of Irving's Beaver Bay 
group, and 'is usually referred to, by him, as "black olivine 
gabbro." 
The Red Rock ineniber. This consists of intrusives and 
their equivalent effusives. The former include granite and 
augite syenite which occur extensively in the region between 
the preceding two members and as bosses and dikes within 
the gabbro. Numerous dikes also cut the Beaver Bay diabase, 
and extensive surface flows of quartz porphyry lie upon it. 
All of the rocks are highly acid. The Red Rock member, so 
named on account of the persistent red color of the rocks, 
succeeds the Gabbro and Beaver Bay Diabase members and 
presents similar physical characters concerning its origin. The 
member includes the red rocks associated with the Saint 
Louis River gabbro, and parts of the Lester River and Beaver 
Bay groups of Irving. 
