GEOLOGY. 401 



The facts here stated, have led many geologists to believe that the 

 earth was once completely melted with fervent heat ; and has been 

 gradually cooling for ages, since elephants lived in Siberia : and that 

 the whole of the interior is still in a melted state ; the central heat 

 still remaining, while the exterior has nearly reached its limit of cool- 

 ing; since no change has been recorded within the period of authentic 

 history. Others deny the doctrine of central heat, and attribute the 

 volcanic fires, which they suppose to be of limited extent, to chemical 

 action, such as the burning of the alkaline metals, by contact, per- 

 haps, with water from the sea. According to this theory, the com- 

 bustion should penetrate deeper and deeper : and this refers us back 

 to a period when the earth's surface might have been heated by ex- 

 ternal fires. Either of these theories may account for the formation 

 of crystalline rocks, by heat and pressure ; as it has been proved by 

 experiment, that such materials may be crystallized by these causes* 

 Either of these theories will also aid in explaining the action of earth- 

 quakes, and volcanoes ; the generation and confinement of gases 

 causing the former, till the gaseous matter finds vent in the latter, or 

 rends new fissures, to make its escape. But farther investigations 

 are yet required, to complete the theory of Geology, and to reconcile 

 all the facts hitherto collected. We can only add, that the book of 

 nature and the book of revelation will, doubtless, when fully under- 

 stood, be found to agree entirely ; both being the work of the same 

 infinitely wise and omnipotent Author. 



4. As a specimen of Descriptive Geology, we have only room to 

 give a general idea of the structure of our own country ; which presents 

 a rich field of geological investigation. It should here be understood 

 that countries are named geologically from the strata which appear on 

 their surface ; though other formations may exist beneath. The greater 

 part of New England, including the White and Green mountains, is 

 of the primary formation ; consisting chiefly of granitic rocks. 

 Rhode Island, and a narrow belt to the north of it, are of the tran- 

 sition formation, but contain traces of coal ; and the red sandstone 

 of the Connecticut river, belongs to the secondary. The Highlands 

 of New York, and the Blue Ridge in Virginia, are primary moun- 

 tains ; but the Catskill, and Alleghany range, are transition : and 

 between these two chains lies the Great valley, chiefly of the se- 

 condary formation. The coal regions of Pennsylvania, Virginia, 

 and Ohio are chiefly transition and secondary ; and this latter forma- 

 tion prevails in New York and the Western States, Coal is found 

 not only in eastern Ohio, but in northern Michigan, western Illinois, 

 on the Wabash and Green rivers, and west of the Arkansas. The 

 coast of the United States, from Long Island southward to Florida, 

 and westward to Louisiana, is alluvial ; widening towards the south. 

 Back of this, is a belt of the tertiary formation, rich in fossil shells ; 

 and still farther back, is an upper secondary, or cretaceous formation, 

 extending nearly to the foot of the primary mountains already re- 

 ferred to. 



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