of American Geologists and Naturalists. 1 
thus lodged in the Brooklyn hills. The number of species com- 
prised in the collection, amounts to ten or twelve, among which 
are those now most common to our shores. 
_ These discoveries in regard to the drift appear to agree with 
those which Sir R. Murchison states to have been found in the 
drift of Europe. They must be admitted as proving that the 
most common species of our present Mollusks were of prior ori- 
gin to the hills where the remains were found, and probably 
older than the entire formation of drift and boulders which is 
found in the Northern States. The species obtained are not such 
as indicate a colder climate than now prevails. But the shells 
ound by Prof. Emmons and others in the Pleistocene clays on 
the borders of Lake Champlain, and by Mr. Lyell and others in 
Canada, appear to belong to a later period of the drift, and Mr. 
Redfield infers that they were brought in from more northern 
regions or from deeper waters, by the great arctic currents which 
must have swept over these regions during the drift period, when 
this portion of the continent was deeply submerged. 
polar currents annually freighted with immense fields and islands 
of floating ice, such as are now diverted along the shores and 
banks of Newfoundland till they are met by the dissolving in- 
fluences of the Gulf Stream nearly in the Jatitudes of Boston 
and New York, he considered to be among the chief agents in 
producing the remarkable phenomena of the drift period. 
10. A Section of the Coal Seams and accompanying Measures 
f the Hazelton coal basin in Luzerne County, Penn., as an 
lustration of the construction and coloring of Geological See- 
ons ; by Prof. W. R. Jounson.—It is most commonly imprac- 
le to take ts di trically across the strata, or at 
ght angles to the plane of stratification ; but yet for many theo- 
retical and practical purposes, an easy and correct method of de- 
termining the thickness of a series of stratified rocks is very im- 
portant. 'T'o compute thickness from observations of devel, in- 
clination, direction of dip, and measures of distance, presupposes 
that the survey is restricted to limits within which the dip, strike, 
and thickness are essentially constant. On the borders of the 
ocean or other tide waters, on the artificial cuttings for railroads 
and canals and even along the margins of many rivers and ravines 
as well as in horizontal mine-tunnels, the measurements may be 
generally made independent of the use of leveling instruments. 
Tn such cases the compass, tape-line and clinometer suffice to give 
the horizontal distance from one member to another in the series, 
together with the inclination and direction of | is 
tee the horizontal measured line is aint to € “gta 
of dip, the degree of this obliquity may be represen y 9, the 
inclination by 7 and the sedewated distance by d. Then ealling 
Cait e=sini xcoso xd. 
Bet Sh 2 
