638 GEOLOGY. MICROSCOPY. 
see no good generic character by which it can be separated. A 
description and figure of this new Passerculus, will be found in the ` 
“ Naturalists’ Guide” (page 112) under the name of Centronys 
Bairdii, with a history of the capture of the first specimen and also 
an account of how this name came to be applied to it. It will like- 
wise be understood that the name of Centronyx Bairdii, given in a 
notice in the May number of the Naturaxist (page 307) by Mr. 
Brewster, should read Passerculus princeps. 
The Thalasseus Havelii, mentioned by Mr. Brewster in the same 
article, should also read Sterna Forsterii, for I have become con- 
vinced by carefully studying a large number of specimens that the 
Thalasseus Havelii = Sterna Huavelii of authors, is the young of 
Sterna Forsteriit. — C. J. MAYNARD. 
GEOLOGY. 
OIL Creek PETROLEUM KNOWN IN THE LAST CenTurY.—At à 
meeting of the California Academy of Sciences, July 15th, Mr. 
. C. Stearns presented a communication, embodying be 
following extract from the Massachusetts Magazine published in 
the year 1789, Vol. i, p. 416, showing that the existence of 
petroleum in Pennsylvania was known at that period : 
“ In the northern part of Pennsylvania, there is a creek — 
halted at this spring, collected some of the oil and bathe 
joints with it. This gave them great relief 
with which they were afflicted. The water o 
drank freely operated as a gentle purge.” 
MICROSCOPY. yrs 
Succrsstve Porarization or Licat.—This curious S0% “ 
procedure has been accomplished in connection with the — 
polarizing microscope, by Mr. J. W. Stephenson. ne gre 
fitting of the polarizer, between the polarizing prism and the 
he places, mounted so as to have a rotating movement py the 
a truncated glass prism having its broadest face pipt Ts 
sugar of milk process, and its other faces so situated eer 
polarized by passing through the Nicol’s prism m oe 
of itso% 
