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East-west section across South Dakota to show the Dakota artesian system. The Dakota sandstone is composed for the most part of well-rounded and well-assorted quartz grains, representing an ancient river and wind-formed sand deposit.

Dakota Artesian System

East-west section across South Dakota to show the Dakota artesian system. The Dakota sandstone is composed…

"The two faults of larger throw, by which a single sheet of trap is represented in three ridges, are proved by the threefold repetition of series of beds comprising sandstone, conglomerate, and amygdaloidal trap, shale, and heavy trap." -Walcott, 1901

Strike Fault

"The two faults of larger throw, by which a single sheet of trap is represented in three ridges, are…

"A fish known chiefly by scales, fossil remains of which are found in Old Red Sandstone." — Williams, 1889

Holoptychius

"A fish known chiefly by scales, fossil remains of which are found in Old Red Sandstone." — Williams,…

This illustration represents a section of the rocks along the river below Niagara Falls. It gives some idea of the alterations which occur in the strata.

Niagara Falls

This illustration represents a section of the rocks along the river below Niagara Falls. It gives some…

A section of the Paleozoic rocks found in the Mississppi basin illustrating the periods and ages.

Paleozoic Rocks

A section of the Paleozoic rocks found in the Mississppi basin illustrating the periods and ages.

Section to show normal progressive overlap of marine formations and their shoreward change from limestones to sandstones.

Progressive Overlap of Marine Formations

Section to show normal progressive overlap of marine formations and their shoreward change from limestones…

Thin section of quartz sandstone shown under the microscope. The original rounded quartz grains are surrounded by new quartz, forming quartzite.

Quartz Sandstone

Thin section of quartz sandstone shown under the microscope. The original rounded quartz grains are…

Marks made by water spreading over shells of stones that are lodged in the sand, in this image in Silurian sandstone.

Rill Marks

Marks made by water spreading over shells of stones that are lodged in the sand, in this image in Silurian…

The marks created in mud or sand by flowing water, often found in sandstone.

Ripple Marks

The marks created in mud or sand by flowing water, often found in sandstone.

Erosion forms of a jointed sandstone.

Sandstone

Erosion forms of a jointed sandstone.

Along the south shore of Lake Superior is a sandstone once regarded as belonging to the Potsdam, but probably, in part , of the age of the Calciferous, in which we search in vain for any of those fossil remains so common in Minnesota. Whaterver its geological age, the Lake Superior sandstone is a formation of remarkable interest. This section across Lake Superior shows (a) water level. (b) trap outburst north of the lake, (c) trap outburst forming Isle Royale, (d) trap outburst forming Kewenaw Point, (e) Lake Superior sandstone and conglomerate. Eözoic and other rocks underlying the sandstone (f).

Sandstone

Along the south shore of Lake Superior is a sandstone once regarded as belonging to the Potsdam, but…

Cross-bedding in Sylvania sandstone.

Sandstone with Cross-bedding

Cross-bedding in Sylvania sandstone.