86 



BULLETIN OF THE 



Lake Superior mineral lands in the trap rocks only, and the valuable 

 veins are limited to a narrow belt of the amygdaloidal variety of that 

 rock." {I c, p. 471.) Mr. J. W. Foster (May 26, 1849, /. c, i)p. 773- 

 785) regarded the sandstone " as resting at the base of all the fossil- 

 iferous rocks." 



In Foster and Whitney's Report to the Laiad-Ofiice {I. c, p. G07), it 

 is stated that " what is generally known as the trap range, consists of a 

 belt of igneous rocks, composed for the most part of hornblende and 

 felspar, which in places have broken through the sandstones, tilting them 

 np at high angles ; but oftener are found in alternating beds, having 

 the same dip as the detrital rocks. The associated sandstone and con- 

 glomerate belong to the silurian system, and rest at the base of all 

 fossiliferous rocks." Concerning the copper it is stated : "Some of these 

 accumulations of copper are mere beds, the result of segregation, while 

 others are contained in fissures, formed subsequent to the containing 

 rock, and associated with a veinstone entirely dissimilar." (I. c, p. 608.) 



The final report of Messrs. Foster and Whitney on the Copper Lands 

 was presented April 15, 1850.* Regarding the trap range of Keweenaw 

 Point, it is stated that " this range does not appear to have been the re- 

 sult of one, but of successive overflows ; for we not only find the igneous 

 materials arranged in parallel bands, and exhibiting great diversity in 

 external characters, but we also find numerous intercalations of con- 

 glomerate of inconsiderable thickness, but extending for miles in a linear 

 direction — these mixed products being associated in regular beds, having 

 a common bearing and inclination, so that the inexperienced observer is 

 inclined to refer the whole to a common origin. This deception is still 

 further increased by observing lines of pseudo stratification in the trap 

 conforming to those of the associated sedimentary rocks." {l. c, p. 61.) 



The southern trap range of the Point is said to consist of "a vast 

 crystalline ma^s, forming an anticlinal axis, flanked on the north by the 

 bedded trap and conglomerate, and on the south by conglomerate and 

 sandstone." {L c, p. 64.) Towards Portage Lake none of this trap 

 was protruded, but it was thought that the same fissure extended along 

 this line from the ''head of Keweenaw Point to the western limits of 

 the district." (/. c, p. 68.) Regarding the relations of the sandstoTie to 

 the trap on Keweenaw Point and Isle Royale, they say : '* As a general 

 observation, the upjier portions of these sandstone belts are much 

 more changed by heat than the lower." {L c, p. 63.) "The upper por- 

 tions of the sheets of trap are highly vesicular, resembling pumice. 



* Executive Documents, 1st Scss,, 31st Cong., 1819-50, IX., Doc. 69, 224 pp. 





i 





■4 

 ■1 



,1 







< - 





J^ 



A 

 i 



J 



7- 



t 



!f 



i 



J- 



xY 



-K 



