42C> REPORT OF NATIONAL MUSEUM, 1904. 



these fissures or ruptures he believed to be due both to the nature of 

 the crust fractured and the direction of the fracturing forces. He 

 accepted the doctrine of an earth cooled from a state of fusion, and 

 regarded the influence of electric currents on the position of conti- 

 nents in process of formation as an established fact. An outer crust 

 having once formed, the deep-seated crystallization would go on at a 

 rate inconceivably slower, and circumstances would be favorable for 

 a coarse crystallization of the material below and for the operation of 

 electrical currents. The rupturing force he believed to be contraction 

 caused by cooling. He argued that a cooling globe incrusted over by 

 refrigeration while contraction was still going on beneath would, like 

 a Prince Rupert's drop, be in a state of tension. Such a tension is 

 bound to produce fractures and displacements, the direction of which 

 would depend on rate of cooling in different parts and on the change 

 in the earth's oblateness accompanying a diminution of its diameter. 

 He concluded, from the absence of volcanoes in the interior of conti- 

 nents, that these portions of the globe cooled first and became solid; 

 the intermediate portions cooling later and at a less rapid rate con- 

 tracted most, since the crust was here thinnest. The oceanic areas 

 would therefore be gradually subsiding and the tension increasing: 

 moreover the tension, from its nature, would be exerted nearly hori- 

 zontally. He inferred, therefore, that the subsiding oceans have pro- 

 duced the mountains of the continents, and that the oceanic and 

 continental areas have never changed places, and saw no reason for 

 appealing to an incomprehensible subterranean force for the uplift- 

 ing of the mountain chains or the continents. Such may have been 

 "only a result on the whole of the deepening of the ocean's bed. 

 It is obvious * * * that the earth has reached its present con- 

 dition by gradual progress from a state of prolonged igneous action 

 through epochs of increasing quiet, interrupted by distant periods 

 of violence, to the present time, when even the gentlest oscillations 

 of the crust have almost ceased." These same ideas he had previously 

 put forward in a paper in the American Journal of Science on the 

 Origin of some of the Physical Features of the Earth's Crust, noted 

 elsewhere. 



In his discussion of the origin of the coal beds of New South Wales, 

 Dana concluded — 



that the layers of the coal series were probably deposited by fresh-waters during the 

 different stages of annual floods and wider deluges occurring at more distant periods} 

 that the subsidence, which may have been gradual during the coal deposits, finally 

 submerged the whole. 



Another important observation bearing on the same subject was 

 made when writing on the geology of Luzon and its coal beds: 



One of the interesting points about this lake (Laguna de Bay) is the fact that vast 

 quantities of plants live on its surface and pass down the river into the bay, carry- 



