APRIL 12, 1901.] 
bromide in equal strength, although it may be 
largely a matter of degree. 
The bath should not be quite so strongly 
alkaline as for negatives, in order to get the 
best results. The best results when pictures 
are developed in daylight are as fine as can be 
obtained in the dark room, in the ordinary 
developing of negatives. Various developers 
have been tried, but none of them have yielded 
as good results as hydrochinon. 
Mr. G. Pauls laid before the Academy a 
branch of a small hackberry (Celtis) which had 
become completely covered with the small nod- 
ular galls frequently borne in smaller quantities 
by the hackberry, and called attention to the 
fact that in this particular case the natural 
enemies of the gall-forming creatures seemed 
to have been absent, allowing of their unusual 
multiplication. 
One person was elected to active membership. 
WILLIAM TRELEASE, 
Recording Secretary. 
GEOLOGICAL SOCIETY OF WASHINGTON. 
_ THE 112th meeting was held March 13, 1901, 
at the Cosmos Club. The following formal 
communications were presented : 
“The Soil Survey of Cecil County, Maryland,’ 
by Mr. C. W. Dorsey. This example of recent 
soil-mapping, by the Department of Agriculture, 
was illustrated by a colored map showing the 
areal distribution of ten classes of soil. 
‘Discussion of Geologic Units—Formation, 
Stage and Age,’ by Messrs. Bailey Willis, H. S. 
Williams and others. 
Mr. Willis, in introducing the discussion, 
briefly reviewed past attempts to consistently 
divide assemblages of stratigraphic rocks into 
units. He pointed out that a clear distinction 
exists between division on lithological grounds, 
and division on paleontological grounds, and 
that this distinction should not be lost sight of. 
He believed that the cartographic unit, the 
formation, should be defined purely on the basis 
of lithological character. In regard to the terms 
used for the units of the lithological, faunal and 
chronological scales in geology, it is highly im- 
portant that there should be unanimity in usage. 
Shall we attempt to reconcile and fix the usage 
of such English substantives as series, forma- 
SCIENCE. 
585 
tion, system, stage, period, ete., or shall we 
adopt entirely new terms from some foreign, 
preferably dead, language, and so avoid tying 
up well known English words to definite re- 
stricted meanings? Several terms from the 
Sanscrit were given in illustration of this sug- 
gestion. Professor H.S. Williams called atten- 
tion to the fact that a formation, as defined on 
purely lithological grounds, lacks true unity. 
Two scales must be used to scientifically de- 
seribe the formations and faunas which the 
geologist studies—a structure scale and a time 
scale. The latter must express definite time 
values. Such values are presented by (1) the 
persistence of equilibrium of a particular fauna, 
(2) the persistence of a particular species, (3) 
the persistence of a genus, etc. Major J. W. 
_ Powell gave his experiences in devising a scien- 
tific nomenclature in psychology. He at first 
endeavored to redefine old words. Readers 
forgot his definitions and unconsciously used 
their own in reading his work. He strongly 
favored the adoption of new terms devoid of all 
confusing connotations. Mr. Whitman Cross 
illustrated the difficulties arising when a forma- 
tion, once defined, is found to thicken and ex- 
pand into several members in another portion 
of the field. He wasemphatically of the opin- 
ion that the evidence of fossils should be freely 
used in addition to lithological distinctions, 
whenever such a course will lead to a fuller ex- 
pression of the structural and historical facts in 
the geology of a given region. 
F. L. RANSOME, 
DAVID WHITE, 
Secretaries. 
BIOLOGICAL SOCIETY OF WASHINGTON. 
THE 337th regular meeting was held on Sat- 
urday evening, March 23d. 
Sylvester D. Judd presented a paper on 
‘Bird Food Problems,’ stating that in studying 
the food of birds as indicated by their stomach 
contents, one was confronted with the problem 
of identifying the articles eaten from very small 
particles. He showed, illustrating his remarks 
with lantern slides, how the presence of grass- 
hoppers, cut worms, the larvee of may beetles, 
earthworms and various plants might be 
recognized under the microscope from minute 
