106 
Psyche 
[June-Sept. 
about two hundred other Creede insects, sent to me for deter- 
mination by Professor Case of the University of Michigan, 
who had previously secured them from Mr. Caplan. All of 
the fossils have been sorted into orders and most of them 
into families or superfamilies. As in the case of the insects 
of the Latah formation and of the Manitoban amber, I have 
referred these Creede fossils to specialists on various groups 
of living insects. Although this procedure tends to delay in 
large measure the publication of the results, it is the only 
way capable of yielding authentic determinations and con- 
clusions. Since several more years may elapse before all the 
specimens of the Creede collection have passed through the 
hands of specialists, it has seemed advisable to publish 
the results in several parts, all under the same general title, 
whenever a sufficient number of manuscripts have been 
completed. The descriptive part of the present paper deals 
with the fossils belonging to the following orders and 
families: Neuroptera (F. M. Carpenter), Isoptera (T. E. 
Snyder), Diptera, Tipulidae (C. P. Alexander), Bibionidae 
(M. J. James), and Syrphidae (F. M. Hull). To these spe- 
cialists and those who are working upon other families I am 
grateful for their indispensable cooperation. 
Since this is the first extensive account of the Creede 
insects, it is pertinent to include a brief discussion of their 
geologic occurrence and environment. The geology of 
Creede district has been thoroughly investigated by Emmons 
and Larsen (1923). According to them, the Creede forma- 
tion was deposited in a lake that occupied a valley carved 
out of the rocks of the Potosi volcanic series. The lower 
part of the formation consists chiefly of fine-textured, thin- 
bedded, rhyolite tuffs, usually light grey or light brown. 
Thicker beds of sandy material, lenses of conglomerate, and 
numerous bodies of travertine are also present. It is this 
lower part of the formation that contains the insects and the 
best plant material. The upper part is of coarser texture 
and consists of well bedded breccia and conglomerate, with 
some fine tuff. The origin of the formation seems to have 
been much like that of the Florissant shales, which lie more 
than a hundred miles to the north-east. Some of the ash 
thrown out by local volcanoes fell into the lake and together 
with sand and mud was deposited at the bottom. Insects 
