178 BULLETIN 109, UNITED STATES NATIONAL MUSEUM. 



numerous and broad dikes, and so altered that in the vicinity of the? 

 trap they can be scarcely recognized. 



Doctor Houghton in this connection makes some observations of 

 peculiar interest in relation to studies in which geologists are at this 

 moment engaged. He says: 



The rocks of the complete northwestern escarpment of this range of hilla 

 Mere evidently in an intense state of ignition while in contact with the sedi 

 mentary rocks, as is clearly shown by the very great changes which have taken 

 place in the rocks last alluded to. In fact, I am disposed to refer the origin of 

 much of the amygdaloid rock to the fusion of the lower portion of the sedimen- 

 tary rocks referred to, for the reason that, as we pass south from this junction 

 the amygdaloid rocks wholly disappear, their place being supplied by green- 

 stone. And again, so intimately ai-e they blended that it is frequently impossible 

 to determine where the amygdaloid ceases and the upper sedimentary rocks com- 

 mence. Fragments of the sedimentary rocks, the characters of which can be 

 clearly recognized, are not of rare occurrence imbedded in the amygdaloidal 

 rock, a circumstance which, although by no means conclusive, should not b« 

 overlooked in considering this subject. (Pp. 27-8.) 



Throughout the entire extent of the " trap range " it is bounded on 

 the north and northwest by hills of conglomerate and sandstones, 

 Hekloin exceeding 400 feet in height. To the northwest of these " a 

 dike of trap is seen to extend for many miles along the line of coast 

 of Kevveenaw Point. It lies in a plane parallel to the stratification 

 of the sedimentary rock by which it is embraced, and with that rock 

 dips to the northwest. The dike is chiefly made up of greenstone, 

 but not unfrequently large portions of the mass consist of amygda- 

 loid in which the amygdules are filled or composed of quartz, chalce- 

 dony, agate, calc spar, zeolite, etc." 



The dikes just mentioned may be regarded as contemporaneous 

 veins. But another class of veins traverses not only a portion of 

 the trap rocks but also the upper sedimentary rocks. These are 

 true veins. 



On He Royale the relative positions of the greenstone and 

 amygdaloid are reversed — the latter lying on the south. The same 

 order is observed on the north shore, and here, also, the hills of pri- 

 mary rock lie farthest from the lake. 



The trap rocks throughout the region are usually distinctly jointed, 

 and where they approximate to the sedimentary rocks there is, 

 not unfrequently, so distinct a cleavage opposed to the joints in di- 

 rection, as to give the appearance of stratification. The columnar 

 structure is rudely presented in a few cases, and tolerably well de- 

 fined columns, having a height of 80 to 90 feet, appear on the north- 

 eastern extremity of He Royale. 



3. Mefamorphic rochi^. — " Flanking the primary rocks on the 

 Fouth, is a series of stratified rocks, consisting of talcose, mica, and 



