The Ashgillian (Upper Ordovician) Montgomery Limestone occurs as slide blocks in melange of the Shoo Fly Complex, northern Sierra Nevada, northern California. Brachiopods and sphinctozoan sponges from the Montgomery Limestone have closest biogeographic ties to coeval faunas of the eastern Klamath Mountains (Yreka terrane), and in the case of the brachiopods, to east-central Alaska (Jones Ridge). The latter was part of North America in the Ordovician. A small collection of Montgomery rugose corals yielded one species that is known elsewhere only in the Yreka terrane and in northern Maine. Montgomery tabulate corals have affinities with contemporaneous faunas of the Yreka terrane, northern Europe/Asia, Australia, and eastern North America. The apparent absence of similar tabulate taxa in western North America may be an artifact of incomplete collecting. As a whole, the biogeographic data indicate that the Montgomery Limestone was deposited close enough to Ordovician North America for faunal interchange to occur, and during its deposition was probably relatively near that continent. A comparison of lithologic units of the Shoo Fly Complex with those of the Yreka terrane indicates that some units in each area have no counterparts in the other (e.g., schist of Skookum Gulch in the Yreka terrane), and other units have general similarities in age (where known) and lithology, but differ in detail. The Yreka terrane has been interpreted as the remnants of an Early Cambrian arc and Ordovician-Devonian arc–fore-arc–accretionary prism, and the Shoo Fly Complex as a fragment of a Devonian or older accretionary wedge. Available biogeographic and stratigraphic data can be reasonably explained, as has been done by earlier authors, by a paleogeography in which the Yreka terrane and Shoo Fly Complex were parts of the same arc-trench system but were situated at different points along the strike of the arc. Lateral changes along strike in tectonic conditions and source areas could account for the observed disparities.

Abstract West of Mississippi River natural gas, in commercial quantities, was first discovered in Miami County, Kansas, in 1877. This and subsequent supply discoveries were from rocks, mostly sandstones, of Pennsylvanian age. As most of these sandstones are lenticular, few gas occurrences are controlled by folding. It is estimated that about 350 square miles of gas-bearing rocks have been discovered since 1900. Occurrences of natural gas in rocks of Pennsylvanian age in eastern Kansas are here, for analytical purposes, divided into post- and pre-Fort Scott. The supply contributed by post-Fort Scott rocks has been small, but pre-Fort Scott rocks have been the major source of natural gas supply. The pre-Fort Scott section of Pennsylvanian rocks is divided into an upper and a lower division. The upper division, consisting of the upper 350 feet of Cherokee formation, covers all of eastern Kansas. In its upper 50 feet are found most of the gas- and/or oil-bearing shoestring sandstone bodies; in the lower part the oil-bearing sandstones of Greenwood and Butler counties. The supply of gas from these formations has not been of major importance. The lower division, with a maximum thickness of about 300 feet, contains many large sandstone bodies (also lenticular) from which natural gas was the dominant product. The important fields, producing gas from the lower division, were located in Allen, Neosho, Wilson, Montgomery, and Labette counties. They are now either abandoned or nearly exhausted. At the contact between the Pennsylvanian and Mississippian systems occurs the Burgess (Hogshooter) sandstone. This sandstone, also lenticular, is extremely erratic in distribution. Where productive, notably at Elk City in Montgomery County, it is very prolific but short-lived. Limestones in the upper 50 feet of the Mississippian system have produced gas in eastern Kansas, notably in Elk and Chautauqua counties on the Longton anticline. Rocks of Ordovician age have yielded very little gas in eastern Kansas. Occurrences of gas in post-Fort Scott rocks are up-dip accumulations, commonly found on plunging anticlines or domes. In pre-Fort Scott sandstones, the entire body may be gas-filled with bottom water, if it parallels isopach lines of the Cherokee formation, but it may be distinctly up-dip with edge and bottom waters where the body pitches with the regional dip. The upper surfaces of pre-Fort Scott sandstone bodies show structural closure (lenticularity) ; the overlying Fort Scott limestones usually show a similar structure, but the underlying Mississippian rocks are usually undisturbed excepting for regional tilting and warping. Gas-bearing areas in rocks of Mississippian age are restricted to anticlines and domes, most of which were folded and partly eroded before deposition of Cherokee sediments. The thickness of Mississippian rocks is everywhere reduced over these folds. Most of the important gas fields in Kansas were discovered and developed prior to the use of surface or subsurface geology. A few important gas fields have been found on surface structure forms, notably at Elk City in Montgomery County; a few were recognized as major subsurface folds before their importance as gas fields was known, notably the Longton anticline.

Abstract This article is aimed at providing an overview of the geology of the Dayton region to those who seek an introduction to Dayton’s geological story. The oldest rocks exposed in the area are Ordovician (Katian Stage, Cincinnatian Series in local North American usage) in age, and are world famous for the quantity and quality of their fossils. Unconformably overlying the Ordovician strata are Silurian (Llandovery–Wenlock Series) dolomites, limestones, and shales, which represent tropical seas that were at times rich in crinoids, corals, brachiopods, and other invertebrates. A large time gap (unconformity) in the rock record of some 420+ million years occurs between the Silurian and the Pleistocene “Ice Age” deposits of the area. Significant changes to the natural environment in the Dayton area have occurred during the Anthropocene. A number of localities that can be reached within about 30–40 minutes from downtown Dayton are described. This is effectively Montgomery County and adjacent counties. As such this treatment is brief and not meant as a compendium but as an introduction and outline of Dayton’s geology and geological history. The localities selected illustrate Dayton’s geological heritage, from the Ordovician to the Pleistocene, while several of the area’s distinctive natural landmarks are discussed. A number of the landforms are expressions of the Niagara Escarpment, where resistant Silurian limestones and dolomites overlie less resistant older rocks.