THE NORTHERN PACIFIC ROUTE. | 9 
Jonathan Carver, in describing his journey to this region in 1766, 
mentions a large cave in the St. Peter sandstone about 30 miles 
below the Falls of St. Anthony, a cave called by the Indians the 
“Dwelling of the Great Spirit.’ In this cave they held religious 
ceremonies, and near it they buried their dead. When the sandstone 
is examiied under a magnifying glass it is found to be composed of 
beautifully white translucent grains of quartz, resembling rock 
candy except that the fragments are round instead of angular. 
The even lines of bedding, which can be seen from either of the 
bridges mentioned, show that the sand must have been laid down in 
water, but the forms of the individual grains show with equal cer- 
tainty that the sand before it was washed into the ocean and deposited 
along the shore was blown about by the wind and perhaps heaped 
into large dunes, such as are now seen around the head of Lake 
Michigan south of Chicago. 
The St. Peter sandstone, on account of its purity, is well adapted 
to glass making and in many places it is used for that purpose. It 
extends from St. Paul southward as far as central Arkansas and east- 
ward as far as Detroit, and probably once extended much farther 
north, but in that direction it has been eroded—worn away by frost, 
rains, and streams—auntil all trace of it is lost. On account of its 
wide distribution and the purity of the materials that compose it, 
this deposit of sand is one of the most remarkable in the world. 
Above this sandstone, if stone it may be called, lies a thin-bedded 
limestone known as the Platteville, which can be seen at the entrance 
to the Wabasha Street Bridge and which was formerly used about 
the ‘‘twin cities’’ for building material. The stone occurs, however, 
in thin layers and does not stand the weather well, so that very 
names are printed. The place of each of the larger units of rock or of time (as Cam- 
brian, Ordovician) in the general geologic column is shown in the table on page 2. 
: Thickness 
Ordovician: in feet. 
Galena limestone (exposed) ps bs 
rah shale ( exposed) Sse 
Platteville limestone ceo etl ee 30 
t Peter \ / 150 
Shakopee dolomite 60 
Oneota dolomite "3060 
oe OEE 
Cambrian 
joa ae sandston j 
St. Lawrence formation 100 
Franconia ee Dresbach sandstone, and under- 
lying roc 
i —— 675 
Red clastic series (Algonkian?)............--------+++-+--++-+* 1, 125 
ranite. pels ies 
