AMERICAN GEOLOGY DECADE OF 18:50-1839. 359 



important rocks. J. I). Whitney served as assistant in the laboratory 

 of the survey. 



As with other of Jackson's reports, this work contained scarcely 

 anything- of a theoretic or advanced nature, although he did suggest 

 that the apparent dipping of the Vermont marble beds under the Green 

 Mountains might be due to "a folding or doubling back of the strata, 

 which may curve around and pass down toward the shores of Lake 

 Champlain, where the same strata may be composed of marine shells." 

 He noted also that the secondary rocks must at some time have been 

 horizontal and formed a continuous deposit extending entirely across 

 the region now occupied by the White Mountains. If, however, the 

 secondary strata were to be restored to their original horizontal posi- 

 tion, he found an insufficiency of materials to cover the gap left by 

 the removal of the primary rocks composing these mountains. This 

 he would ascribe to the breaking up of the secondary rocks at this 

 point through the sudden elevation of the primaries and a more or less 

 altering of the same by heat. 



It was Jackson's idea, as set forth in this report, that highly 

 inclined stratified rocks could have been made to assume that position 

 only by some distorting cause other than aqueous action. This cause 

 he conceived to be "a deep-seated power residing in the interior of 

 the crust of the globe,"' the power itself being furnished by the 

 "great caldron of molten rocks and pent up gases and steam, there 

 being no more difficulty in our conceiving of the adequacy of this 

 force than in the prodigious power of steam in moving the enormous 

 engines" daily seen in operation. He conceived that a better idea of 

 this power might be gained if one " look to the dimensions of the 

 earth's great boiler, and consider the comparative thinness of its 

 sides." Volcanoes he devoutly referred to as safety valves which 

 prevented a general upbursting of volcanic tires, and "hold all in the 

 most perfect order, and preserve the earth in safety." 



His views regarding the glacial drift would seem to have undergone 

 no appreciable change since 1839, although perhaps somewhat dif- 

 ferently expressed in the later reports. He wrote of this drift as due 

 to the "ocean waters and seas of ice from the polar regions having 

 been hurled with violence over the surface of the northern hemisphere 

 during a period of shallow subsidence." The drifting of bowlder- 

 laden icebergs would account for the glacial strhe, but the glacial 

 theory of Agassiz he looked upon as quite insufficient and absurd. It 

 is to be noted, however, that his only conception of glaciers was that 

 of mountain glaciers of the Swiss type, the onetime presence of 

 which was disproved by the nonradiating character of the drift and 

 striae. This glacial flood to which he now appealed, however, was not 

 regarded as contemporaneous with the Noachian deluge, but as having 

 occurred before the advent of man. 



