At the Fishtrap ferry, one and three-fourths miles south, and half a mile east of Lagonda, coal appears in the bank of the stream just above low-water mark. It is mined a little for local use. Section XXV. AT FISHTRAP FERRY NEAR LAGONDA Altitude of coal about 665 feet A. T. FT. IN. 1. Shale, blue, argillaceous, becoming darker below..... 2. Shale, black, slightly fissile.. 6 3 Interval to top of Lower Coal Measures about 5 feet. The thickness of the coal, as also the presence of the shale parting, is given on the authority of the owner, as high water covered the opening at the time of our visit. We correlate this with the Macon City coal. The presence here of a shale parting, as also the thickness of the overlying shale, is exceptional. As exposed, the bed shows more resemblance to the Bevier coal than to the higher seam. We are led to make the above correlation, however, from the evidence presented by the Lagonda shaft, where the Macon City coal is at about the same horizon. This is further corroborated by an outcrop of limestone, resembling the Macon City limestone, at the bridge. over Puzzle creek, about three-quarters of a mile west of the ferry. The limestone crops out 5 to 10 feet above the horizon of the coal. Half a mile north of the bridge is another limestone outcrop, 25 feet above the last, which probably represents that overlying the Summit coal. THE QUATERNARY GEOLOGY. By J. E. Todd, Assistant Geologist. The region covered by this sheet lies wholly within the great plain of the extra-morainic or marginal drift, which extends from northeastern Nebraska to southeastern Illinois. Its features and structure are quite simple. The main irregularities are the result of more recent erosion attendant upon its relation to the branches of the Chariton river. As it is near the divide between the tributaries of the Mississippi and Missouri rivers, wider areas of the original flat surface are found than further west. For the same reason, more of it lies at a high level. The Topography. The upland, which is at an altitude of about 850 feet, is quite even and level. Undulations of more than five feet are rare, and all undulations are very broad and gentle. As one goes toward the streams, in some places, the even surface very gradually declines, but more frequently there is a well-defined edge whence begins an abrupt descent. The former occurs most often when following an elongated promontory of the upland which projects between secondary valleys; the latter in other cases, especially when approaching the head of a ravine or valley. Sometimes a "flat," as we may call a separate flat area, may be found 50 or 60 feet below the upland level. These may not be classed, however, as terraces, because they seem to have no correspondence to each other; they seem rather the result of settling and sliding, than of original deposition. This supposition seems, moreover, to be borne out by their structure. The Chariton river, with its branches, has cut valleys 125 to 175 feet deep in this plain. These valleys are bordered with low bluffs and, along the main stream, are sometimes over two miles wide. Traces of a terrace or "second bottom" are found lower down on the main stream, but have not been noticed in the region described. The "arborescent" arrangement of the valleys and probable erosion from a plain gently sloping to the south become quite evident from a study of the hypsometric map on page 6. It should be noted in this connection that but one shade indicates the surface between 700 and 800 feet. In short, while the main topographic features are the work of simple erosion, the secondary are traceable to the sliding and creeping of the clayey deposits resulting from the attenuation of ridges, and the consequent effects of moisture and gravity. The bed rock of the region, as is described on other pages, is of Coal Measure age, consisting largely of clays, shales, and marly limestones. Its surface seems to have been tolerably even, at least there were no prominent elevations. The earthy or superficial formations, which are probably all Quaternary, are, (1) the pre-glacial or basal clay, (2) the drift, boulder clay or till, and (3) the gray or loamy clay. This is their chronologic order. The distribution of these is shown in the opposite page plate. 1. The Pre-glacial or Basal Clay.-Under the drift clay, which is perhaps the most conspicuous formation of the region, there has been observed at several points a light gray clay, with a bluish tinge where it has not been long exposed. It is without northern pebbles; in fact may well be described as pebbleless. In color and texture it closely resembles the "gray loamy clay" (3). It is not very often seen. It is generally covered by the drift clay, and, when exposed, is apt to be mistaken for rearranged material of the gray loamy clay. For these reasons it seems not to have been, hitherto, recognized. Even now we could wish that its relations were more clearly established. One of the clearest exposures was noted at the foot of the railroad grade west of Macon, in the ditch on the north side of the track. There, 8 to 10 feet of it are seen overlain by pebbly drift clay, 2 to 4 feet thick. The junction between, for a rod or two, is distinct, even and horizontal. It is about 25 feet higher than the top of Carboniferous shale exposed in an old quarry several rods northwestward. The base of the basal clay was nowhere observed, nor has it been seen very near exposures of bed-rock; but, from the facts stated above, it is estimated to be sometimes 25 feet thick. No fossils have been found in it.. Less instructive exposures of this formation have been noted in similar relations east of Macon, west of Moberly and near Higbee. It seems not improbable that "No. 3, Blue Clay, hard," of the Bevier section, No. II, given on the preceding page 15, and also Nos. 4 and 5, or at least the latter, of the "Black Diamond section," No. XI on p. 25, may be of this formation. Samples of these sections have not been directly examined. 2. The Drift or Till.-The next formation in order is an unstratified, pebbly clay, similar to that largely developed farther north. Its prevalent color is a yellowish brown, but the yellow is usually more decided in the upper portion and where it has been exposed. Lower down it is more of a reddish tinge, while below, especially where it has not been subject to infiltration of surface waters, it is of bluish drab or even of quite dark leaden hue. Moreover, although it cannot be defi nitely divided into different members, there is considerable difference in composition and texture between upper and lower portions. Above it is looser and usually more loamy, and there is a tendency to a stratified arrangement; below it is usually more clayey, more compact and more stony, especially near the base. It is generally divided by joints into irregular polygonal masses, hence is often popularly called "joint clay." Not infrequently these joints are occupied by carbonate of lime, sometimes in sheets which have been found inch thick, and sometimes in irregular concretionary nodules. Sometimes the joints are blackened with oxide of iron. Along the upper boundary of the blue portions, that color is frequently found to obtain in the interior of the polygonal masses before mentioned, while the surface of the same is tinged buff next the joints. The erratics scattered through the clay are mostly of crystalline rocks, granites, greenstones, and a red quartzite, evidently identical with the Sioux quartzite of southwestern Minnesota. These last seem not to be distributed much farther east than this area, though they are found as far south as southeastern Boone county, in considerable numbers. Limestone boulders are occasionally found, but they do not clearly belong to the local strata. In fact, we find few or no local boulders or pebbles in the drift clay except near its base. The erratics are frequently planed or striated, showing that they have come fresh from glacial agencies; they are quite evenly though rather sparsely distributed through the clay, yet boul. |