Agassiz.J 104 [June 16, 



for a site where they were invariably at work the following spring, 

 commencing these dams in some cases where their dams were dis- 

 turbed in winter, they would migrate bodily and establish themselves 

 on the shores of a more isolated creek. They invariably build burrows 

 when first starting their dams, and when the ground of the bank is 

 not propitious they continue to dwell in them and do not build lodges, 

 as was the case in a mud dam built across a rather steep valley where 

 the flowage simply gave depth near the dam, and at a considerable 

 distance from it, only spreading into a shallow sheet at too great a 

 distance from the dam, evidently, to make that mode of inhabitation 

 available. 



The extent of the denudations of forests, thus artificially produced 

 by the beavers, is quite extensive ; the areas of some of these beaver 

 clearings are very large. I have seen ponds of an extent of no less 

 than forty acres, as the direct result of the backing water of a beaver 

 dam, and beaver meadows of two to three hundred acres in area are 

 by no means uncommon. When beaver dams are placed one below 

 the other, as is frequently the case, the extent of country thus opened 

 and cleared of forests by them may cover the large portion of several 

 sections of land, changing into open swamp lands extensive tracts, 

 which at one time must have been dry, and covered with dense 

 forests. This interference of beaver dams is also frequently the 

 cause of accumulations of water on ridges, from which the natural 

 water sheds are altered. From talking with intelligent trappers who 

 have hunted in the lands of the Hudson Bay Company, I learn that 

 the works of the beavers are so extensive there in some localities, that 

 they have played a not unimportant part in changing the whole aspect 

 of large tracts of the country, and covering with water a great extent 

 of country which was once thickly wooded. 



On the Habits of a few Echinodeems. By Alex. Agassiz. 



In the various reports of animals found at great depths in the 

 ocean, the presence of starfishes attached to the rope at a considera- 

 ble distance from the dredging or sounding apparatus, has been 

 instanced as proving beyond doubt that they lived at great depths, 

 and that the rope was dragging along the bottom, as their specific 

 gravity was so much greater than that of the water that when placed 

 in it they immediately sank. My object is simply to record a few notes 

 of what I have observed on the seacoast at various times with refer- 



