418 REPORT OF NATIONAL MUSEUM, 1904. 



This, it will be noted, is radically different from the idea put forward 

 by Agassiz. 



The conglomerate composed of rounded fragments of jaspery rock, 

 so abundant throughout the copper region of the south shore of the 

 lake, they regarded" as a friction conglomerate, testifying to the 

 "■intensity of the force with which the eruptive rocks have been pro- 

 pelled from the interior through the earth's crust,"" the detritus hav- 

 ing been redistributed by the waters, following in this the teachings 

 of Von Buch. Their graphic account of the conditions under which 

 it was supposed to have been formed is worthy of being reproduced 

 entire: 



We may suppose that at one time all of this district (i. e.,the copper district) 

 tunned a part of the bed of the primeval ocean. Adopting the theory of a cooling 

 globe, we may further suppose that the waters were in a heated condition and dif- 

 fered essentially in chemical composition from those of the present oceans. The 

 earth's crust was intersected by numerous powerful fissures, and the communication 

 between the exterior and interior was unobstructed. Volcanic phenomena were 

 much more frequent and exerted on a grander scale. Each volcanic paroxysm would 

 give rise to powerful currents and agitations of the water, and their abrading action 

 in detaching portions of the preexisting rocks, and depositing them in beds and lay- 

 ers on the floor of the ocean, would operate with greater intensity than at the pres- 

 ent time. We can trace the remains of one volcanic fissure extending from the head 

 of Keweenaw Point, in a southwesterly direction, to the western limits of the dis- 

 trict, and of another, in a parallel direction, from the head of Neepigon Bay to the 

 western limits of Isle Royale. Along the lines of these fissures existed numerous 

 volcanic vents, like those observed at this day in Peru, Guatemala, and Java, which 

 were characterized by periods of activity and repose. From these vents were poured 

 forth numerous sheets of trap, which flowed over the sands and clays then in the 

 progress of accumulation. During the throes and convulsions of the mass portions 

 of rock would become detached and rounded simply by the effects of attrition, and. 

 jets of melted matter be projected as volcanic bombs through the air or water, which, 

 on cooling, would assume spheroidal forms; while other portions of the rock, in a 

 state of minute mechanical division, would be ejected in the form of ashes and sand, 

 which, mingling with the water, would be deposited as the oscillations subsided 

 among the sands and pebbles at the bottom of the sea. During the whole of this 

 period of volcanic activity the sands which now form the base of the Silurian system 

 were in the progress of accumulation and became mingled with these igneous 

 products. The level of the sea, as evidenced by the ripple marks, was subject to 

 repeated alterations; sometimes it rose so shoal that the marks of the rippling waves 

 were impressed on the sands, at others it sank to unfathomable depths. 



In the process of consolidation the rocks became traversed by numerous fissures, 

 and the water, charged with lime, was forced in like jets of steam, filling them with 

 materials different from the inclosing mass. In this way the pores in the conglom- 

 erate and the vesicles of the amygdaloid were filled. 



. The formation of the copper and silver ores they regarded as duo 

 probably to electro-chemical agencies. To quote their own words: 



The existence of two metals side by side, like copper and silver, each chemically 

 pure and capable of being alloyed in any proportions; the accumulation of the latter 

 near the cross courses or at the junction of two mineral planes; the changes in the 

 metallic contents of lodes in their passage through different rocks, and the parallel 



