wii.LiAMs.1 rogers's classification. 85 



xr . . Feet. 



Vergont scries: 



Vergeut Flags, Portage flags of New York 1,700 



Vergent shales, Chemung group of New York 3 200 



Ponent series : 



Ponent Red sandstone, Catskill group of New York 5, 000 



Vespertine series: 



Vespertine Conglomerate and sandstone 2 GGO 



Umbral series, or Carboniferous shales and limestone : 



Umbral Red shales and limestone 3 000 



Serai series, or Coal strata : 



Serai Conglomerate, or lowest division of Coal Measures 1, 100 



Lower Productive Coal Measures. 



Lower Barren Coal Shales. 



Upper Productive Coal Measures. 



Upper Barren Coal Shales. 



The numbers corresponding to the names here proposed are as fol- 

 lows: 



XII. Serai. VI. Pre- Meridian. 



XI. Umbral. c Scalent. 



X. Vespertine. ' ( Surgent. 



IX. Ponent. IV. Levant. 



VTTT $ Vergent. HI. Matinal. 



V111, \ Cadent. II. Auroral. 



VII. Meridian. I. Primal. 



In 1850 H. D. Rogers 1 discussed the coal formations of the United 

 States, considered from the following points of view: 



First. The source, stratigraphical relations, and conditions of depo- 

 sition. The land-derived deposits, attaining a maximum thickness of 

 1,400 feet in the southeast, thin out westward to less than 100 feet, and 

 the Coal Measures gradually thicken toward the northwest. The im- 

 mense range and horizontal extension of the conglomerates and coal 

 seams prove that it could not have been deposited by any local estuary 

 or deltal actions, but along a broad, shallow sea shore, which was dis- 

 turbed by violent interior forces, producing enormous undulations. 



Second. The author discussed the structural conditions and position 

 of the anthracite basins, and found them arranged in two systems of 

 flexures, the larger series with an amplitude of many miles and a length 

 of 100 miles, with average direction of about N. 75° E., the smaller 

 series trending N. 70° E. 



Third. He treated of the metamorphism of the anthracite coal-bear- 

 ing strata, showing it to be more complete in the east, the products of 

 the western region being bituminous and those of the east anthracitic. 



Fourth. Erosion is considered. 



Finally, a summary of the statistics of the coal fields is presented, 

 in which the author states that the productive area of the anthracite 

 fields of Pennsylvania does not exceed 200 square miles, with an aggre- 

 gate thickness of 100 feet. 



1 On the coal formation of the United States, and especially as developed in Pennsylvania. Proo. 

 Am. Assoc, vol. 4, 1850, pp. 65-70. 



