Geology of tlic St. Croix Dalles. — Berkey. 153 
Glaucoidte. An earthy granular bright green mineral 
occurs abundantly in the Dresbach formations. It is recog- 
nized as glauconite and is the same mineral that is so abund- 
ant in the St. Lawrence formation of many localities.* 
Kaolin. This mineral is present in small quantity as an 
accompaniment of the process of alteration. A few speci- 
mens, however, have been obtained in which kaolin is the chief 
resultant of decay. This particular line of alteration seems 
to have been of limited extent, as suggested in a previous 
paragraph, and is most noticeable in the conglomerates of the 
Dresbach formation. 
Apatite. Phosphoric acid is abundant in the lower sedi- 
mentary strata of this area. The Lingulepis shells give strong 
tests for this compound and in the green-sand bed number- 
less microscopic apatite crystals have been developed as a sec- 
ondary mineral constituent. The phosphoric acid reaction is 
readily obtained from the Obolella (green-sand) bed and also 
from the Lingulepis (calcareous) shale. Although these mic- 
roscopic crystals are very perfectly and abundantly developed, 
no individuals of larger size have yet been observed. 
Sulphates. The efflorescence formed on the exposed 
pyritiferous Dresbach shales at the carding mill, Taylor's 
Falls, has proven quite complex in its composition. The re- 
sults of an analysis made by Mr. H. A. Webber, a student in 
the University of Minnesota, is as follows: 
Si Og 12.Q46 per cent. 
FegOg 22.828 " 
Aig O3 , ' 4.141 " 
KgO 1.844 " 
Nag 4.659 " " 
CaO 2.210 " " 
SO3 32.500 " " 
H3O 17.840 " 
Organic matter traces 
Total 98.968 per cent. 
This analysis is similar in complexity and general range to 
voltaite (Dana, p. 927), but it is not identical with any known 
mineral. It is apparently a mixed substance. The most puz- 
*Magnesian Series of the Northwestern States. Bull. Geol. Soc. of 
America, vol. V, 1895, P- I72. 
