Re-view of Recent Geological Literature. 189 
geologic formations, Dr. Grant advises that the altitude of the base 
of the Galena limestone, and possibly also of the base of some other 
formations, as the St. Peter sandstone, should be everywhere approx- 
imately indicated. 
The geologic series, nearly horizontal in bedding, extends from the 
Potsdam sandstone upward to the Niagara limestone, which caps a few 
isolated mounds ; and the whole series represents essentially contin- 
uous deposition. There is no sure evidence that the district received 
any rock formations after the Niagara period. During the Ice age it 
was exempted from glaciation, being a part of the large driftless area 
of southwestern Wisconsin and the edges of adjoining states. It formed 
a low peneplain, nearly at the sea level, during Cretaceous or early Ter- 
tiary time; but subsequent elevation caused the streams to erode wide 
valleys 100 to 400 feet, or more, below the uplands. The amount of 
this erosion is about equal to the masses left between the valleys, so 
that the general Tertiary denudation thus known averages about 200 
feet for the entire district. A considerable amount of earlier denuda- 
tion is also known to have taken place, for the thickness of residuary 
soil and clay on the broad upland tracts averages about thirteen feet, 
which would correspond to a removal of 100 feet or more of the lime- 
stone strata. 
The ores mined are galena, sphalerite, and smithsonite, occurring 
chiefly in cracks or crevices of the Galena and Trenton limestones. 
They also occur in brecciated or very porous parts of the limestones, 
and as deposits disseminated in some places at and near the junction 
of these formations. The original ore deposition is attributed to deep- 
seated or artesian water circulation, supplemented later by the ore-de- 
positing action of the shallow downward circulation of surface waters. 
Although the ores near the surface have not yet been exhausted, the 
future mining development is expected to be mostly at greater depths. 
Dr. Grant thinks that the lower seventy-five feet of the Galena lime- 
stone, with the next few feet at the top of the Trenton limestone, con- 
tain larger quantities of zinc ore than have yet been produced in this 
district. w. u. 
Palaeontologische Notizen, 3-6. vox Carl YYimax. [Bull. Geol. In- 
stitut. of Upsala. no. II, Vol. VI, part I, 1902.] 
3- Uber Robergia micro ptJialmus Lurs. und Triarthrus jemtlandicus, 
Lurs. 
It is refreshing to be taken back to the times behind Linnaeus for 
an author who is worthy to have his name perpetuated, not in perennial 
brass, but in a new generic name for a peculiar trilobite Laurentins 
Roberg (1715) taught in the university of Upsala before Linnaeus. 
He was a naturalist who gave some attention to fossils and described 
trilobites as remains of crabs. 
This species, Robergia micropthalmiis, had been described both by 
Linnarsson and Brogger as a Remopleurides ; Holm supposed it similar 
to Dicellocephalus serratus, with an extension of the cheek in front 
of the glabella, but Wiman found there was no such extension. The 
