Contributions to Geology 6.2

The analysis of coarse clastic grains using standard statistical methods

DONALD O. DOEHRING and ERIC N. CLAUSEN Department of Geology, University of Wyoming, Laramie, Wyoming

Pages
87-92

Keywords
statistical, particles, sampling, clastic, sand, sieving

Abstract
The analysis of sand and larger size particles by the use of direct measurements and least square statistics is advocated. Sieving techniques introduce systematic and nonsystematic errors which reduce their usefulness. Sieving of the sand particles unnecessarily groups the data, thus causing a loss of information. Other errors introduced by sieving techniques can be attributed to the actual mechanics of sieving, the operator, and the computational analysis, particularly when empirically derived formulas are used.

It is proposed that direct measurements be made on a relatively small number of randomly selected grains. Measurements of some properties can be made from photographs of grains or on the stage of a microscope. Statistical analyses should employ either the definitional or computational formulas for the least square moments. If a digital computer is available calculations become a trivial matter.

A comparison of sieving methods with the standard statistical methods demonstrates that the standard approach is more accurate. Measurement and sampling precision for the standard method were tested and found to be adequate for distinguishing between particles deposited in slightly different environments. The suggested approach permits gathering of all desired data in one operation, produces more accurate results, prompts the user to design a well thought out sampling scheme, produces least square statistics which can be used for statistical inference, saves time and costs, can handle measurements of any property, and allows simple yet meaningful comparisons of results obtained by different workers using different equipment.

Invertebrate burrows in the non-marine Miocene of Wyoming

HEINRICH TOOTS Department of Geology and Geography, C. W. Post College, Greenvale, NY

Pages
93-96

Keywords
burrows, invertebrate, Wyoming, Taenidium

Abstract
Burrows of invertebrates referable to "Taenidium" have been found in massive sandstones of the Sheep Creek Formation near Wheatland, Wyoming. The burrows show an internal fabric indicating backfilling of abandoned parts of the burrow. The presence of the backfilling fabric supports assignment of the burrows to the feeding burrows (Fodichnia).

The burrows are associated with lacustrine sediments. The burrows were formed either in very shallow parts of a lake or in a paludal environment representing the transition from lacustrine to fluviatile (floodplain) sedimentation.

Animal remains from Horned Owl Cave, Albany County, Wyoming

JOHN E. GUILDAY, HAROLD W. HAMILTON, and ELEANOR K. ADAM Carnegie Museum, Pittsburgh, Pa.

Pages
97-100

Keywords
mammals, Horned Owl, Wyoming, pika, vole, Equus

Abstract
Fragmentary remains of twenty-five species of mammals were found during the course of the 1966 excavations at Horned Owl Cave. Camel, Camelops, and a large species of horse, Equus, are extinct. Mountain goat, Oreamnos, no longer occurs in Wyoming. Pika, Ochotona, and spruce vole, Phenacomys, do not occur in the vicinity of the cave today. The remaining species are characteristic of the area today or in the recent past.

A computer program with computes modal and mineralogic compositions within a ternary system

KENNETH PERRY, JR. Department of Geology, University of Wyoming, Laramie

Pages
101-118

Keywords
Fortran, modal, mineralogical, composition, ternary, chemical

Abstract
This program is designed to compute the mode and the chemical composition of each of the coexisting mineral phases in the modal assemblage within a ternary system at constant temperature and pressure. The program is written specifically with reference to the system SiO2-FeO-MgO at 1 atmosphere and 1150 degrees C. It is easily modified, however, to compute within the chemical composition spaces of this system at other temperatures. In addition, by substituting appropriate mathematical expressions for the mode and composition of individual mineral phases, the program can be modified to represent any ternary system.

The program is written in Fortran IV language for the Philco 2000 computer.

A cross section of the alluvium and bedrock at the Laramie River in Laramie, Wyoming

JAMES OTTO DUGUID Department of Civil Engineering, AFIT, University of Wyoming, Laramie

Pages
119-122

Keywords
Laramie River, cross sectin, alluvium, Wyoming, terraces, Kaycee, Moorcroft, Lightning

Abstract
A cross section of the Laramie River obtained by geophysical techniques and checked by a number of drill holes indicates that the alluvial deposits of the Laramie River are thinner than suggested by Leopold and Miller's work on alluvial valleys in Wyoming. Three alluvial terraces are present on the Laramie River. However, a more detailed analysis of units within the alluvium itself should be made before the names Kaycee, Moorcroft and Lightning are applied to the terraces of the Laramie River.

Petrologic reconnaissance of the Precambrian rocks in Wind River Canyon, central Owl Creek Mountains, Wyoming

KENT C. CONDIE Department of Earth Sciences, Washington University, St. Louis, Missouri

Pages
123-129

Keywords
Wind River, Owl Creek, Wyoming, intrusive, Precambrian, metasomatism, metamorphism

Abstract
The Precambrian rocks in Wind River Canyon are composed of hornblende-plagioclase and hornblende-cummingtonite amphibolites, biotite-quartz schists, and a quartz monzonite intrusive and its associated granitic dikes and pegmatites. The section is metamorphosed to the amphibolite facies of regional metamorphism. The massive character and comparatively mafic composition of the hornblende-plagioclase amphibolites suggest that they are ortho-amphibolites; a more silicic and alkalic composition and the occurrence of uniform layering in the hornblende-cummingtonite amphibolites suggest that they are para-amphibolites. Potash feldspar and sodic plagioclase in the amphibolites and schists surrounding the quartz monzonite intrusive are interpreted to have resulted from incipient Na and K metasomatism which accompanied emplacement of the intrusive.