Page:The Journal of geology (IA journalofgeology21894univers).pdf/197

the stratigraphy of Missouri coal seams is lead to believe that the different veins diverge from one another in a manner best explained by the preceding diagram, the dotted line representing post-Carboniferous erosion. (Figure 2).

These conditions also accord in the main with the facts observed in all the Western coal fields.

An attempt to harmonize the two seemingly very divergent and even contradictory theories is apparently fruitless. But a more careful examination of the subject shows that the two theories are manifestly not based on facts taken from the same point of view, but from quite different positions. Andrews' idea may be taken as representing a cross section of the coal bearing strata taken parallel to the general course of the shore; Winslow's a section at right angles.

In districts where mountains are being elevated, orographic movements in the earth's crust continue to be felt for long distances from the line of maximum disturbances. If a great sea or an ocean occupies a region affected to a moderate extent by the oscillations, an extended shore line trends approximately with the axis of the mountain system, for the more important minor corrugations commonly run in similar parallel lines. The direction of maximum change in the inclination of strata is therefore at right angles to the axes of the folds, and hence in a broad way perpendicular to the shore line. The direction of minimum change in tilting is, under ordinary conditions, the same as the axes, or parallel to the shore. Bearing these suggestions in mind geological cross sections, under favorable circumstances of examination, would show a general parallelism of coal beds when made in one way; a decided tendency to non-parallelism when constructed in the other.

Granting, then, an old, uneven land surface, such as is known to have existed in Carboniferous times in the upper Mississippi basin, with the waters of the sea and the marginal maritime flats gradually creeping inland, it would naturally be expected that in the case of any one of the marshy plains skirting the shores for any great distance there would be a very tortuous boundary on