NA TURK OF COAL HORIZONS. I 79 



succession. The faunal and floral features are practically identi- 

 cal from one end of the great coal basin to the other. 



The greatest interest, economically and geologically, in the 

 Carboniferous basin centers around the coal deposits. Their 

 disposition perhaps comes first in importance, both from the 

 standpoint of the operator and of the geologist. The subject is 

 certainly one of wide-reaching import. 



There is now abundant evidence to show that the Western 

 Interior coal field at the time of deposition was for the most 

 part a broad, shallow basin opening to the westward into the 

 great continental sea which then occupied most of what is now 

 known as western North America. That the Coal Measures of 

 the region were laid down during a period of gradual, prolonged, 

 though often checked, subsidence is evidenced by all stratigraph- 

 ical and lithological details, as well as by the characteristic 

 faunal peculiarities. That the coal beds originated largely in 

 coastal swamps of limited breadth but, with some interruptions, 

 of very considerable length, stretching out near sea level for 

 long distances and sending out minor extensions into the old 

 rivers and estuaries is fully warranted by the facts disclosed 

 everywhere. On the low, slowly sinking shores there prevailed 

 at certain times a similarity of physical conditions especially 

 favorable to coal formation. During these intervals unusual 

 amounts of coaly material were allowed to accumulate and to be 

 preserved in places, the period being preeminently one of coal 

 growth, at least for a given province. The great stratigraphic 

 plane marking each record may be appropriately termed a "Coal 

 Horizon." 



In stratigraphy, a geological horizon is a level recognizable 

 over a considerable geographical extent, having a more or less 

 well defined stratigraphical position, distinctive as to lithological 

 features and characterized by a particular set of fossils. The 

 term in a broad sense is almost equivalent to formation, and has 

 been used as indefinitely. In its more limited meaning it is 

 applied properly to a minor part or zone of the smallest strati- 

 graphical unit having a commonly accepted specific name. Un- 



