714 HISTORICAL GEOLOGY. 



the reduction, in the case of anthracite, would be to about one eightli, as 

 above estimated. The average amount of ash in anthracite ought, conse- 

 quently, to be nearly half greater than in bituminous coal. 



The production of the anthracite of eastern Pennsylvania was referred to 

 the action of heat on ordinary bituminous coal first by H. D. Rogers, on the 

 ground of the upturned and flexed condition of the rocks in that part of 

 the state. The upturning fades out to the northwestward, and the Wilkes- 

 barre anthracite region is on its outskirts. The heat produced in the rocks 

 by the upturning need not, for the result, have been either great or much 

 prolonged ; moreover, it would have spread laterally from the area of great- 

 est disturbance, more or less far into the outskirts, as is well exemplified in 

 various metamorphic regions. The following are other facts favoring this 

 origin of the anthracite: (1) The coal of the upturned and more or less 

 metamorphic Coal-measures of Rhode Island is the hardest of anthracite. 

 (2) The coal of the Carboniferous Coal-measures of ivestern Pennsylvania, 

 and that of the states farther west, where the beds are nearly horizontal, is, 

 throughout, bituminous coal and not anthracite. (3) Variations in the con- 

 ditions of the coal-making areas over the globe have led to various kinds 

 of coal without making anthracite. BroAvn coal, or that containing a large 

 percentage of oxygen, is known to form where there is much access of air ; 

 and cannel coal, a kind rich in oil-producing hydrocarbons, and little oxygen, 

 under conditions of prolonged steeping beneath a deep covering of sediments ; 

 for all the characters of the beds associated with cannel coal indicate, as 

 Newberry held, the fact of such a steeping of the bed of vegetable debris. 

 These are the extreme results, except that more remarkable extreme, the 

 loss of all the oxygen through union with carbon, and thereby the making of 

 hydrocarbon oil or gas as the substitute for coal. Anthracite is not known 

 among the products so made, except in regions of upturned rocks, or in the 

 vicinity of igneous rocks. Graphite, a grade beyond anthracite, is formed 

 from the excessive heating of mineral coal, as is proved in the metamorphic 

 coal regions of Rhode Island, Worcester, and elsewhere. 



GENERAL OBSERVATIONS ON THE PALEOZOIC ERAS. 



GROWTH OF THE AMERICAN CONTINENT. 



1. Facts connected with its growth. — The facts which have been presented 

 sustain the view that the American continent throughout Paleozoic time was 

 gradually growing in its rock formations and dry land, and thereby extend- 

 ing from the Archaean nucleus southeastward and southward, but not much 

 in a southwestward direction. It is manifest, also, that after the Lower 

 Silurian era had passed, the growth took place mainly through processes at 

 work over the great Continental Interior, — a vast American Mediterranean 

 Sea, bounded on the north, northeast, and east, by Archaean confines. More- 

 over, the eastern areas of progress in New England and beyond had like- 



