As stated in the introduction, the purpose of this paper was twofold: To determine 1) the underlying geologic cause of the features, and if possible, 2) the reason for the features� appearance in the first cover measured by the satellite.

Despite their appearance in the first cover of vegetation, the circular and arcuate features seen on the MSS satellite image probably have an underlying geologic cause. Their general northwest trend, association with slopes and drainage, both on the surface and below, and location within the Missouri Gravity Low at its intersection with the 38th parallel lineament all support this conclusion. The exact nature of that cause, however, remains difficult to ascertain. One theory which is explained by the available data involves a Precambrian fracture along which calderas form. Following collapse of their central portion over the emptied magma chamber, mafic plutons are introduced along the fractures at their margins, having first ascended through the older fractures underlying the caldera sites. A second theory postulates that the intrusions are peripheral to a collapsed laccolith in the basement. Well control is not such that either of the above hypotheses can be confirmed.

The reason for the appearance of the features on the image is more difficult to determine. If the underlying cause of the features is a difference in basement composition, as suggested above, an explanation must be found for why this difference should be apparent through at least 1500 feet of sedimentary cover. Although no system of fractures has yet been found on the surface, there is a correlation between the features of interest with both surficial stream valleys and an elongated low on the structural contour map of the top of the Cambrian [Fig. 4.3]. Both of these are erosional surfaces of karsted terrain. In addition, a slight correlation exists between the circular features and concentrations of sinkholes at the surface. One possible answer might be that a set of arcuate fractures has propogated up from the basement rocks into the overlying strata. Differential erosion of the soluble carbonates along these fractures may be what has caused the observed pattern. As field work for this paper was limited to observation of cultural or other obvious features, further field study is suggested in order to determine whether such a fracture system does indeed exist.