Search USGS⌕ Search

Geology topics

John T. Hack

Publications and source records attributed to John T. Hack.

7 recordsLinked to original sources
USGS2017

The Finley Site: Antiquity of the Finley Site

This report is based on two months reconnaissance in the summer of 1941 in the Eden Valley, Wyoming. The work is as yet far from complete and the conclusions presented here must be regarded as tentative. It is hoped that in the future more extensive geological work may be undertaken. The Finley site provides a promising opportunity for a determination of the age of the Yuma culture. The points and bones described by Dr. Howard occur in a culture layer which has been found in a large dune area, here called the Killpecker dunes. The deposition of the culture layer is one of a series of events in the dune area which can be correlated with the cutting and filling of gravel terraces in the Eden Valley to the west, and these in turn may be related to the glacial chronology in the Wind River Mountains which lie to the north.

Wyoming↗
USGS1988

Landforms of the United States

The United States contains a great variety of landforms which offer dramatic contrasts to a cross-country traveler. Mountains and desert areas, tropical jungles and areas of permanently frozen subsoil, and deep canyons and broad plains are examples of the Nation's varied surface. The presentday landforms the features that make up the face of the Earth are products of the slow sculpturing actions of streams and geologic processes that have been at work throughout the ages since the Earth's beginning.

Report↗
USGS1973

Stream-profile analysis and stream-gradient index

The generally regular three-dimensional geometry of drainage networks is the basis for a simple method of terrain analysis providing clues to bedrock conditions and other factors that determine topographic forms. On a reach of any stream, a gradient-index value can be obtained which allows meaningful comparisons of channel slope on streams of different sizes. The index is believed to reflect stream power or competence and is simply the product of the channel slope at a point and channel length measured along the longest stream above the point where the calculation is made. In an adjusted topography, changes in gradient-index values along a stream generally correspond to differences in bedrock or introduced load. In any landscape the gradient index of a stream is related to total relief and stream regimen. Thus, climate, tectonic events, and geomorphic history must be considered in using the gradient index. Gradient-index values can be obtained quickly by simple measurements on topographic maps, or they can be obtained by more sophisticated photogrammetric measurements that involve simple computer calculations from x, y, z coordinates.

Journal of Research of the U.S. Geological Survey↗
USGS1969

Landforms of the United States

The United States contains a great variety of landforms which offer dramatic contrasts to a crosscountry traveler. Mountains and desert areas, tropical jungles and areas of permanently frozen subsoil, deep canyons and broad plains are examples of the Nation's varied surface. The present-day landforms the features that make up the face of the earth are products of the slow, sculpturing actions of streams and geologic processes that have been at work throughout the ages since the earth's beginning.

General Information Product↗
USGS1966

Circular patterns and exfoliation in crystalline terrane, Grandfather Mountain area, North Carolina

Aerial photographs of areas of crystalline rock in the Piedmont and Blue Ridge of western North Carolina reveal numerous large-scale arcuate, circular , and elliptical patterns with diameters from 1000 to more than 4000 feet. They are commonly defined by curving streams, curving ridges, and curving belts of contrasting vegetation. Geologic mapping shows that the circular patterns are not related to primary geologic structures; circumstantial evidence indicates that they are related to exfoliation or sheeting. Rock spalls up to half a mile in diameter may be formed by dilation of the rock as the erosion surface is lowered. The spalls enable tectonic joints to open, forming thin layers of rock of differing permeability and susceptibility to erosion. Exfoliation is probably involved in the erosive process and is probably more important than has been realized, especially in crystalline terrane .

North Carolina↗
USGS1963

Origin of some intermittent ponds on quartzite ridges in western North Carolina

Several intermittent ponds and closed depressions as much as 200 feet wide occur on the crests of ridges in gently dipping Cambrian(?) quartzites in the southeastern foothills of the Blue Ridge Mountains near Morganton, North Carolina . The unconsolidated fill and debris in the ponds consists of clayey sand and saprolite with accessory minerals that could have been derived entirely from the quartzite . The pond water contains appreciable quantities of dissolved silica and with the aid of organic substances could have formed the depressions by solution since the beginning of the Pleistocene.

North Carolina↗