. Studies in natural history. Natural history; Natural history. 66 IOWA STUDIES IN NATURAL HISTORY levels. Wide areas of the plain lie on the Prairie du Galena, Platteville and Niagara formations respectively. The St. Peter sandstone underlies patches of the plain in very small areas only, and the Maquoketa formation is not known to form summit flats at all. In traveling from north to south three distinct belts are crossed, in each of which there are large upland remnants of the Dodgeville plain and between which there is none. (Figs. 13 and 14) Assuming that the Dodgeville plain is a
. Studies in natural history. Natural history; Natural history. 66 IOWA STUDIES IN NATURAL HISTORY levels. Wide areas of the plain lie on the Prairie du Galena, Platteville and Niagara formations respectively. The St. Peter sandstone underlies patches of the plain in very small areas only, and the Maquoketa formation is not known to form summit flats at all. In traveling from north to south three distinct belts are crossed, in each of which there are large upland remnants of the Dodgeville plain and between which there is none. (Figs. 13 and 14) Assuming that the Dodgeville plain is a geometrical plane, it is possible to ascertain its dip and strike if the relative positions and altitudes of three points on the plane forming a triangle are known. If the elevations of a cer- tain strati graphic horizon under the three points on the plain can be ascertained it is also a simple matter to com- pute the dip and strike of the strata and get the relative directions and amounts of dip of plain and strata (Fig. 15). Plain 1300" A Stratum I2401. C Plain 1250' ^^_: j «4 >+M< Stratum 1000* ^*^i0 pla,n *zo° B stratum uoo' Fig. 15. Diagram showing how the dip and strike of a plain and of a stratum can be determined if the positions and altitudes of three points are known. A, B, and C are three points on the surface plain at 1300, 1200, and 1250 feet respectively. On the line AB there is a point D at which the altitude is the same as at C, 1250'. The line CD is the strike of the plain. The direction of dip is obtained by constructing line EB at right angles to CD through B. Reading the direction of EB the dip is found to be S 14° E. From E to B the surface falls 50'. Scaling EB the amount of dip of the plane is found to be ' per mile. Knowing the elevations of a stratigraphic horizon under points A, B, and C to be 1240, 1100, and 1000 feet respectively, locating the 1100' point on AC at F, BF becomes the strike of the strata, the dip CG is S 37° W, and t
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectnaturalhistory, booky
