Hagen.] 134 [January 22, 
Section of Entomology. January 22, 1879. 
Mr. Edward Burgess in the chair. Thirteen persons 
present. 
Dr. H. Hagen read the following letter to Mr. Henry 
Edwards from Mr. Dean, about flies in a petroleum lake, 
Santa Cruz Co., Cal. 
The habitat of these flies is at the south eastern corner of Santa 
Cruz Co., Cal. The immense coast range here ceases at or near the 
right bank of the Pajaro River, the river passing by the mountain at 
this point without any sudden fall. The mountain is composed of a 
very new sandstone filled with shells, many of which yet lie in the 
stream. There is also a whitish shale, a little piece of which I in- 
close, which contains fossil shells different from those of the sand 
stone; this shale I suspect, without having examined it, to be in some 
degree infusorial.+ 
At the immediate foot of the mountain is a lake of probably 
twenty to thirty acres area. In winter and spring this lake is full of 
water which becomes more strongly alkaline by evaporation toward 
the latter end of summer when the lake becomes nearly dry, its bed 
being then covered several inches deep with white layers of carbonate 
of soda. 
On the north side of the lake are copious petroleum springs 
which continually pour out their tar, and this drying has formed 
masses of asphaltum overlying the soil and running down into the 
lake. The petroleum forces passages through this asphaltum forming 
little pools of about the consistence of molasses. 
The flies in question exist in myriads, and appear to breed upon 
the water plants covering the surface of the lake, which are left 
incrusted with the salt and covered with the empty shells of the in- 
sect. The flies sent you were caught with one sweep of the hat, 
probably more than a pint were so caught. ‘They were sitting upon 
the petroleum and piled up upon one another in vast numbers just 
like flies upon molasses, those underneath die and become imbedded 
in the petroleum and are succeeded by others which in turn are 
pressed down into the liquid tar by those above. On approaching 
them they rise in a cloud about two feet above the petroleum, and on 
1 IT was not able to find infusoria. Dr. H. 
