NATURE OF COAL HORIZONS. 1 83 



the stratigraph}^ of Missouri coal seams is led 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 the- 

 ories 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 dis- 

 tances 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 direc- 

 tion 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 exam- 

 ination, 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 



