REPORT OF FOSTER AND WHITNEY 319 



At a later date (1856), however, Whitney was more favorable to an 

 aqueous sedimentary origin of some of the ores of Lake Superior. While 

 not abating from his first view of the igneous origin of the most of the 

 ore ill its present condition, lie said : 



"There is still Muotlier form of deposit which is not infrequently met with in 

 the Lalve Superior re^jjion. . . . This consists of a series of quartzose beds, 

 of great thickness, passing gradually nito specular iron, which frequently forms 

 hands of nearly pure ore. alternating with hands of quartz more or less mixed 

 with the same substance. . . . These deposits seem to have been of sedi- 

 mentary origin. . . . The iron ore may have been introduced either by subli- 

 mation of metalliferous vapors from below during the deposition of the siliceous 

 particles, or by a ])recii)itation from a ferriferous solution in which the strati- 

 tied rocks were in process of formation." ^ 



This suggestion of a ferriferous solution in a part of the waters of the 

 ocean has been widely extended and adopted and appears in most of the 

 latest literature, and has been so far expanded by some that it is made 

 to operate even in all those ore masses in which no trace of sedimentary 

 action could be seen by WTiitney. 



From the time of Whitney to the time of Irving, but few geologists 

 entered thoroughly into the subject of the origin of the Lake Superior 

 ores. Xone were found who disagreed seriously with Whitney, except 

 Charles Whittlesey. Most of them, however, favored the sedimentary 

 hypothesis rather than the eruptive. But frequently some modification 

 or special action was found necessary in order to account for local condi- 

 tions which were thought to be exceptional. Thus T. B. Brooks invoked 

 the alkaline waters of thermal springs.'^ D. H. Browne would modify 

 the sedimentary hypothesis, so far as it required the original deposition 

 of crystallized siderite and calcite, by assuming that the deposit was hy- 

 drous oxide of iron and carbonate of lime.'^' Harrington suggested that, 

 instead of chemical deposition and subsequent concentration, some of 

 the stratified magnetites were deposited at first as iron sands, "just as 

 they are forming in the Gulf of vSaint Lawrence today, the material being 

 derived from the disintegration of preexisting crystalline rocks." ^ Hunt 

 believed that the oxides of iron, when abundant enough to constitute ore 

 masses, were for the most part due to oxidation of the sulphide and the 

 carbonate of iron, these having been formed as constituent parts of the 

 stratified rocks.' Kimball added the idea of subsequent metamorphism 

 in order to account for the specular form of oxide, but suggested that 



^ American Journal of Science, vol. xxii, LS.jO, pp. 8.S-44. 



* Geological Survey of Michigan, vol. ii, 1873, p. 298. 

 ^ American .Tournal of Science, vol. ii, 1889, p. 209. 



* Geology' of Canada. 1873-1874, p. 194 et seq. 



"American Assoc-iniion for the Advancement of Science, August 28, 1880. 



