500 
PHILOSOPHICAL SOCIETY OF WASHINGTON. 
1887, for the purpose of auditing the accounts of the Treasurer, 
respectfully report as follows : 
We have examined the statement of receipts, including dues, 
sales, and interest, and find the same to be correct. 
We have examined the statement of disbursements, compared 
it with the vouchers, and find that they agree. 
We have examined the returned checks, which agree with the 
bank book, the balance of which, as reported by Riggs & Co. on 
December 28, was $942.05, agreeing wdth the Treasurer’s report. 
We have examined the United States and other bonds belong¬ 
ing to the Society, and find them to be in amount and character 
as represented in the Treasurer’s report, aggregating $3,100. 
John S. Billings. 
C. O. Boutelle. 
James C. Welling. 
Mr. George F. Becker presented a communication on the 
Rounding of Rock Masses by External Attack. 
Mr. J. W. Spencer read a paper on the Iroquois Beach—a 
Chapter in the Geological History of Lake Ontario. [Abstract 
published in Science , vol. 11, p. 49.] 
312th Meeting. January 21, 1883. 
The President in the chair. 
Thirty-seven members and guests present. 
The following communications were presented: 
Determination of Fault Hades, by Mr. Bailey Willis. 
[Abstract.] 
Mr. Willis suggested the application of methods of descriptive geometry 
to the determination of hade, and illustrated by statement of results ob¬ 
tained in East Tennessee. 
The method rests on the assumption that the fault surface is a plane for 
short distances, and under this assumption the strike and hade may be 
found after ascertaining by survey the relative positions of three points of 
the fault outcrop. A check is afforded by using a large number of points 
in adjacent sets of three each, and a conception of the fault surface may 
be obtained by extending adjacent plane facets thus determined, either 
