400 REPORT OF NATIONAL MUSEUM, 1904. 



of islands, are interrupted ranges consisting of overlapping lines, 

 either straight or curved, and that curves constitute an essential feature 

 of the system." He showed that throughout the system of outlines 

 presented by the earth northwest and northeast lines are prevalent, 

 and that these lines are usually curved, instead of conforming to the 

 direction of a great circle. He apparently accepted the theory that 

 the course of mountain ranges, islands, and coast lines is attributable 

 to the courses of former fissures in the earth's surface, and, in discuss- 

 ing the electrical, contractional, and other theoretical causes, suggested 

 that if, as claimed, curves of magnetic intensity on the earth's surface 

 are approximately isothermal lines, they must also be lines of equal 

 cooling and hence of equal contraction and tension. But whatever 

 may have been the origin of the fissures, he thought there could be no 

 doubt but that a kind of cleavage structure, or at least capability of 

 fracturing easily in two directions, was given the crust during its 

 formation. 



The conclusions which appear to flow from the facts that have been presented are 

 as follows: 



That the general direction and uniformity of the grand outline features of the globe 

 may be in a great degree the simple effects of the earth's cooling, this operation 

 resulting in (1) solidification, and under the circumstances, whatever they were, an 

 attendant jointed structure or courses of easiest fracture, in two directions nearly at 

 right angles with one another, both varying according to the rates of cooling in dif- 

 ferent parts; and (2) occasioning tension in the crust through the contraction going 

 on beneath, with some relation to circular areas, but especially to large compound 

 areas, which tension caused ruptures conforming or not to the lines of jointed struc- 

 ture according as the force of tension acted in accordance with this structure or 

 obliquely to it. (3) The age of mountains can not, therefore, be determined neces- 

 sarily by their courses; a different direction in a particular region in different ages is 

 not improbable, since the same contracting area might exert its horizontal force in 

 somewhat different directions at different epochs, or other such areas might cooperate 

 and exert a modifying influence; and at the same time an identity of direction for 

 different ages was to have been expected. 



Prof. James I). Dana was born in Utica, New York, in 1813, and was, 



therefore, practically contemporaneous with James Hall. He became a 



student of Professor Silliman's in 1830 at Yale College, leaving in 1833, 



somewhat in advance of graduation, to avail himself 



sketch of j. d. Dana, of an offer to cruise in the Mediterranean, as instructor 



in mathematics to the midshipmen in the Navy. 



The first paper in his bibliography was published in 1835 and gave 

 an account of Vesuvius as seen by him during this trip in 1831. In 

 1836 he returned to New Haven, remaining for two years, the latter 

 part of the time as assistant to Professor Silliman. It was during this 

 time, scarcely four years after his graduation and when but twenty- 

 four years of age, that he brought out his first System of Mineralog\ r , 



