96 ALEXANDER AGASSIZ 



attempts, with the best local talent, failed lamentably. 

 Father tells me that he saw some of your original photo- 

 graphs of dams. Is it possible to obtain a copy of the 

 Grass Lake Dam? I should like very much to possess 

 some remembrance of them more tangible than my notes 

 and collections. If you can help me in procuring a copy 

 from your negatives, if still in your possession, I shall 

 appreciate it greatly. 



Not long after this, he published a short article cor- 

 roborating Mr. Morgan's view, that the beaver did not 

 live in nearly such large communities as was popularly 

 supposed, and that the very considerable results of their 

 labors should be attributed to time, rather than the 

 number of individuals at work. From the depth of the 

 deposits of peat above the beaver dams about Calumet, 

 he estimated that several of these colonies must be at 

 least nine hundred years old. Some of the beaver ponds 

 there covered an area of forty acres, with beaver mead- 

 ows about them of two hundred or three hundred acres 

 cleared from the virgin forests. Where there were dams 

 one behind another, these meadows sometimes covered 

 a large portion of several sections of land. 1 In convers- 

 ing with intelligent trappers of the Hudson's Bay Com- 

 pany he learned of places in Canada where the beaver 

 had changed the character of very considerable portions 

 of the country. 



Besides his studies on the Pourtales collections, he 

 made, during the winter of 1868-69, considerable pro- 

 gress on his " Revision of the Echini ; " but the pressure 

 of overwork, anxiety, and hardships at Calumet had 

 undermined his health, and his work was forced to be 



1 Six hundred and forty acres. 



