1 84 THE JOURNAL OF GEOLOGY. 



the land side and a somewhat less sinuous line on the seaward 

 side ; on the one hand were probably low hills and uplands send- 

 ing out spurs here and there which cut off one marsh from 

 another and often allowing long open stretches of low upland to 

 reach out even to the waters of the sea itself ; on the other hand 

 were often narrow coastal plains rising scarcely above sea level, 

 but, to a great extent, shutting off very effectually the saline 

 waters from the swamps. Viewed areally, the productive por- 

 tion of one of the great coal horizons is a wide irregular zone 

 running in a tortuous course around a more or less extensive 

 portion of the margin of a coal bearing basin included within 

 the limits of a geological province. Examined at the present 

 time coal horizons present, with all the irregularities of original 

 deposition, subsequent change and deformation, a quite different 

 aspect from the ideally perfect level of the ancient surface or 

 zone which existed during the period of formation. In one 

 direction, parallel to the shore, there is a series of minor- saucer- 

 shaped basins strung along on about the same great stratigraphi- 

 cal plane. They may rise or fall as the other strata change 

 in inclination. They may be separated by wide stretches of 

 sandstone or shale, or may come together in places. In the 

 different basins the original vegetable materials in becoming 

 compact shrink most in bulk in the middle, thus allowing the 

 margins to remain considerably higher than the center. This 

 is more noticeable in small basins than in large ones. Then, 

 too, the fact that the direction of minimum movement in the 

 changes of level was, as has been shown, parallel to the pre- 

 vailing trend of the shore does not preclude even in this direc- 

 tion a certain amount of tilting of the strata either by the rising 

 or the sinking of one portion of the shore more rapidly than 

 another ; or by the passage of some of the minor folds in direc- 

 tions not strictly harmonious with the general movement. 



When a new cycle of vegetable accumulation took place the 

 coastal swamps would again spread out at sea level, but not neces- 

 sarily on planes exactly parallel to the horizon previously formed. 

 Horizons which were separated to very considerable distances by 



