Scientific Intelligence — Zoology. 177 



and 80 on, sometimes to a great number. I find that these terraces 

 occur in successive basins, formed by the approaches of the moun- 

 tains upon the banks at intervals. Sometimes the basin will be 15 

 or 20 miles in width, but usually much narrower ; and it is upon 

 the margins of these basins that the terraces are formed. I have 

 rarely found terraces more than 200 feet above the river, which 

 would be in Massachusetts, about 300 feet above the ocean, and at 

 Hanover, N.U., about 560 feet. Nowhere do they exist along any 

 river, unless that river has basins. As to the materials of which 

 they are formed they appear exceedingly artificial. The outer or 

 highest terrace is generally composed of coarser materials than the 

 inner ones. They are all composed of materials which are worn 

 from the rocks, but the outer terrace oftener is full of pebbles, some 

 of them as large as 12 inches, while the materials of the inner seem 

 reduced to an impalpable powder, like the soil of a meadow which is 

 overflowed during high water. Whence did these materials origi- 

 nate ? The materials were first worn from solid rocks, and after- 

 wards brought into these valleys. The outer terrace appears to have 

 been often in part the result of the drift agency. Afterwards, the 

 river agency sorted the materials, and gave them a level surface, the 

 successive basins having at that time barriers. The inner terrace 

 appears to have been, at least in its upper part, the result of deposi- 

 tion from the river itself. 



" I will now mention a few facts which I have observed. The 

 terraces do not generally agree in height upon the opposite sides of 

 the valley. The higher ones oftener agree, perhaps, than the lower 

 ones. If formed, as I suppose, from the rivers, we should expect 

 this. The terraces slope downwards in the direction of the stream. 

 The same terrace which, near South Hadley, is 190 feet above the 

 river, slopes until, at East Hartford, it is only 40 feet above the 

 river, thus sloping 150 feet more than the slope of the river 

 itself, in a distance of 40 or 50 miles. This shows that they 

 could not have been formed by the sea or by a lake, for they would 

 then have been horizontal. The greatest number of terraces ob- 

 served is eight or nine. Generally there are but two or three." 

 President Hitchcock then gives his view of the precise mode in which 

 these terraces were formed, illustrating them by references to other 

 parts of our country, and concludes by a notice of the erosions of the 

 earth's surface. — Annual of Scientific Discovery ^ 1850, p. 229. 



ZOOLOGY. 



10. Fossil Crinoids of the United States. — At the meeting of the 

 American Association, 1849, a paper on the fossil crinoids of Ten- 

 nessee, by Professor Troost, was read by Professor Agassiz.* The 



* These fossiliferous remains were discovered in the carbonaceous and Silu- 

 rian strata of the State, and shew a wonderful development of that form of ani- 



VOL. XLIX. NO. XCVII. — JULY 1850. M 



