416 REPORT OF NATIONAL MUSEUM, 1904. 



of different characters, traversing the older rocks in various direc- 

 tions.' 1 He found six systems of these dikes, to the trend of which the 

 various lake shores in a general way conformed. The relationship of 

 the various copper deposits he attempted to explain on the somewhat 

 remarkable, as well as ingenious, assumption that the material had 

 been poured out in a melted condition, and, cooling quickly, remained 

 in the native state, offering to the agencies of change a relatively small 

 surface exposed in proportion to its mass. At a distance from the 

 main mass, where the ejections were small with relatively large sur- 

 faces exposed, they became more or less completely changed into 

 oxides, sulphides, carbonates, etc. The reader need scarcely be 

 reminded that authorities to-day hold quite a different view, and 

 regard the copper as having been precipitated by reduction to a native 

 state from salts held in permeating solutions. 



Naturally, Agassiz's views, as here set forth on the glacial phe- 

 nomena of the region, are of paramount interest. He argued that the 

 drift of all northeast America and northwest Europe was contempora- 

 neous and due to a general ice sheet. Through a repetition of many 

 of his former arguments he showed that a current of water sufficiently 

 powerful to transport the large blocks found would have swept prac- 

 tically over the entire globe, and not have stopped abruptly, as did the 

 drift, after reaching latitude 39° north. This limit of distribution of 

 the bowlders to the northern latitudes also indicated to his mind that 

 the matter of climate was an important factor. Water-transported 

 material, he further argued, would not cause straight furrows and 

 scratches, and the theory that such might be due to drifting icebergs 

 was rejected on the ground that existing bergs were insufficient, and 

 to produce such as were would necessitate a period of cold sufficient 

 for his hypothetical polar ice cap.' He pointed out that the northern 

 erratics were rounded and widespread; that the highest hills were 

 scratched and polished to their summits, while to the southward the 

 mountain tops had protruded above the ice sheets and supplied the 

 glaciers with their load of angular bowlders. He also called attention 

 to the absence of marine or fresh water shells from the glacial (ground 

 moraine) deposits, showing it was not subaqueous. Referring to the 

 stratified deposits overlying the drift, he wrote: 



The various heights at which these stratified deposits occur above the level of the 

 sea. show plainly that since their accumulation the mainland has been lifted above 

 the ocean at different rates in different parts of the country. 



And, further: 



It must be at once obvious that the various kinds of loose materials all over the 

 northern hemisphere have been accumulated, not only under different circumstances, 

 but "luring long-continued subsequent distinct periods. To the first — or ice period — 

 belong all phenomena connected with the transportation of erratic bowlders, polish- 

 ing, scratching, etc., and during which the land stood at a higher level. To the 

 second belong the stratified drift, such as indicate a depression of the continent. 



