668 FOSSIL INSECTS FROM THE ROCKY MOUNTAINS. 
probably belonging to a different genus. The two forms men- 
tioned under the name of Issus, one from Richardson’s shales and 
the other from Chagrin Valley, are not congeneric; and the same 
is probably true of the ants from these shales and from Fossil 
anon. It is in the Mycetophilide and Tipulide, however, that 
we find the closest resemblance between the different collections; 
in the comparative abundance and variety of these insects, the 
shales worked by Mr. Richardson may best be compared to those 
of Fossil Cañon, but in the former the specimens are too poorly 
preserved to make a close identification very satisfactory ; the genus 
Dicranomyia is apparently found in all three localities. Compar- 
ing the assemblages of species, we find that Diptera and Coleop- 
tera are the prevailing forms in each,* but that within these 
groups the types differ in a remarkable manner, according to their 
several localities ; the Orthoptera and Neuroptera, the spiders and 
Myriapoda of the later discovered beds are wholly wanting in the 
earlier ; the Lepidoptera and Physopoda are found only in Fossil 
Cañon, and no trace of ants appears in Chagrin Valley, though 
occurring in the other two places and also in the locality examined 
by Dr. Hayden. : 
` These results should not surprise us, since in the two rich 
quarries of GEningen, Baden, one of which is only a mile distant 
from, and about one hundred and fifty feet above the other, the 
insects are found to be specifically distinct throughout. Probably 
some of these conclusions will be modified by a more searching 
study of the remains under examination; unquestionably they 
will be altered by further researches in the field; and certainly 
these tertiary beds of the Rocky Mountains appear exceedingly 
rich in insect remains, and are worth careful exploration ; that 
they extend over several successive geological stages seems p? 
able from the great diversity of character in these fragmentary 
collections, and also from Prof. Denton’s statement that the shales 
in which they occur have a thickness of a thousand feet. 
* All the insects as a rule are rather small in size. 
