Geology of the St. Croix Dalles. — Berkeij. 
377 
floor to tlie uppermost member of the sandstone present in the 
St. Croix valley. Therefore each outcrop must be studied b}" 
itself and its position determined independently of the mere 
fact of its conglomeratic character or the proximity of other 
exposures. 
The reason for the extended attention given to the conglom- 
erates in proportion to their geographical extent, lies in the 
fact that within them is preserved the richest fauna thus far 
discovered in all the formations. The loose sandstones which 
constitute so great a part of the sedimentarj'^ strata are un- 
favorable for the preservation of fossil forms. The greater 
part of the shales is almost as barren as the sandstones, and 
such layers as do carry fossils, whether sparsely scattered or 
in multitudes, exhibit a narrow range of species. It is only 
in the conglomerates, as recent observations prove, that there 
existed comparatively favorable conditions for preservation. 
Among these rocks a remarkably abundant and new fauna has 
been discovered. Further description of these new forms 
will constitute a separate chapter of this paper. 
ClassifiGation. A detailed study of the area at and adjacent 
to the Dalles of the St. Croix suggests the following forma- 
tional subdivisions: 
Magnesian 
SERIES. 
(Hall and 
Sardeson. 1 
Shakopee dolomite. 
New Richmond sandstone. 
Oneota dolomite. 
Jordan sandstone. 
St. Lawrence dolomites and shales. 
3. Franconia sandstone (100 feet). 
Basal 
Sandstone J 
SERIES. 
(Modified 
from Norton, i 
2. Dresbach 
shales (150 
feet). 
I Obolella po- \ ^^f °- 
,-i 1 sands 
lita zone ] j i , 
I ( and shales 
J 
Lingulepis i Calcareous 
I pinnaefor- ] & pyritifer- 
1^ mis zone. ( ous .shales. 
The 
St. Croix 
Formation . 
(Winchell.) 
1. The lowest formation of this series is not exposed in 
the Dalles area, hut it includes the lowest sandstone 
beds and possibly also the ''Hinckley sandstone," 
i (0 to 1,000 feet). 
Chapter IV. Geology of the Igneous Mocks. 
A majority of the outcrops of igneous rocks lie within the 
erosion valley of the St. Croix river and thus owe their pres- 
