C. H. Hitcheock on Impressions on Clay. 391 
the river with his barometer, the agency of the periodical barome- 
_ tne changes would also be perceived by their effects upon his 
determinations of elevation. [I am supposing in this case of 
imagined barometric heights, that such an observer would have 
no corresponding observations at the sea level, and that the height 
of the barometer at the mouth of the Amazon would be consid- 
ered a constant. 
. The mean monthly heights of the barometer at Para, as ob- 
served by Dewey in 1846, 1847, and 1848, and till May, 1849, 
showed an extreme range of only 0-41 in., viz.: from 30-02, 
which was the monthly mean for July, 1846, to 29-61, which 
was the monthly mean for September, 1846. : 
he fluctuations arising from the monthly barometric changes 
might give the line of descent along the Amazon, as determined 
in this way, a wave-like appearance, amounting, perhaps, to 300 
or 400 feet at most. But in the case before us, the change actn- 
ally amounted to something like 2,000 feet. For after Herndon 
had descended the river 707 miles, and approached with its cur- 
rent the sea level 571 feet, he was then 1,589 feet higher than he 
was when he set off. 
We cannot, therefore, well conceive how we could find from 
such a source as daily or monthly changes in the uniform baro- 
Metric pressure of Para, such anomalies in barometric determina- 
tions, heights, and pressures as were observed. 
If the suggestion, that the high boiling point of Herndon and 
the high barometer of Castlenau at Nauta were caused by the pres- 
sure of the Trade Winds against the Andes, should turn out cor- 
rect, and the barometric observations on the head waters of the 
Amazon, both of HumboMt and Condamine, tend to confirm it, 
will not the Andes be converted into an immense anemometer, 
by which the force of the Trade Winds may be determined ; and 
if their force, consequently their velocity also ? 
Arr. XXXIX.—Jmpressions (chiefly Tracks) on Alluvial Clay, 
in Hadley, Mass.; by Cuartes H, Hircucocx of Amherst 
re, - 
‘ : Colleg 
Sit ect i 
Tectly south of Hadley Centre, and a short distance north of 
Shepard’s Island. ‘The bed lies 
Vial sand, which abounds in ferruginous tubular concretions. By 
the action of freshets, a large amount of the sand lying upon the 
al + has been removed, leaving about two or three acres of level 
su exposed. ‘The bed itself is close by the place described 
