140 TJic Anicrican Geologist. March, isos 
Mention is made of the sandstone conglomerate in another 
chapter. The pebbles of this conglomerate are well rounded 
and of the ordinary sandstone type. A few small grains of 
diabase are found in it. The cementing substance is calcare- 
ous, but it does not usually produce a rock of great resistance. 
In the present condition of both pebbles and matrix a sand- 
stone is formed which, in common with all the sandstones of 
this area, is too friable for any but the most transient struc- 
tures. 
A specimen of quartzyte was taken from the St. Lawrence 
near a contact of the sedimentaries with the diabase. But 
such a development is extremely local in extent. ' 
Basal Sandstone Series. This term is used throughout 
the paper for a group of sandstones,* shales and conglomer- 
ates, situated between the St. Lawrence formation and the 
underlying igneous floor. These sandstones and shales of 
the St. Croix Dalles area, as is shown in a former chapter, are 
separable into three lithologically well defined subdivisions, 
the uppermost being a sandstone, the middle one composed of 
a glauconitic sandstone and green shales, and the lowermost 
including the calcereous, pyritiferous, and argillaceous shales. 
But below all these, though not exposed in this area, is a thick 
sandstone f which in many other localities constitutes more 
than one-half of the total thickness of the series. J 
The upper member, the Franconia sandstone, is a rather 
tine grained quartz sandstone. The uniform white color 
varying locally to brown or yellow through ferric oxide stains, 
the rather angular character of the grains, the porous and 
friable nature of the stone, the development of minute mica- 
ceous flakes among the sand grains, the complex veining pro- 
duced locally by infiltrated iron oxide, a thick-bedded struc- 
ture exhibited by exposed blufifs, thin seams of greenish clay 
shale frequently magnifying the bedded appearance and the 
general lack of calcareous matter are characteristic of the 
*Owen: Geological Survey of Wisconsin, Iowa and Minnesota, 
1852. p. 49. 
Chamberlin: Geol. Wis., vol. IV, 1882, p. 39. 
Wiuchcll: Final Report Minn. Geol. Survey, vol. II, 1888, p. 407. 
Hall and Sardeson: Bull. Geol. Soc. Am., vol. Ill, 1892, p. 338. 
tGeol. Wis., vol. I, 1883, p. 121. 
tC. W. Hall, Artesian Well-boring in S. E. Minnesota. Bull. Minn. 
Acad. Nat. Sciences, vol. Ill, no. i, 1889, p. 138. 
