26 



TERTIARY INSECTS OF NORTH AMERICA. 



Judging from the present physical condition of the basin, its age is 

 marked as later than the movements which closed the Cretaceous epoch and 

 earlier than the last upheaval in the Tertiary, which seems to have taken 

 place during or after Miocene times, but there are no physical data yet at 

 hand to warrant definite conclusions on this head. 



The insects preserved in the Florissant basin are wonderfully numer- 

 ous, this one locality having yielded in a single summer more than double 

 the number of specimens which the famous localities at.Oeningen, in Bava- 

 ria, furnished Heer in thirty years. Having visited both places I can tes- 

 tify to the greater prolificness of the Florissant beds. As a rule the Oen- 

 ingen specimens are better preserved, but in the same amount of shale we 

 still find at Florissant a much larger number of satisfactory specimens than 

 at Oeningen, and the quarries are fifty times as extensive and far more 

 easily worked. 



The examination of the immense series of specimens found at Floris- 

 sant has not yet critically covered the whole field. It may, nevertheless, 

 be interesting to make the single comparison with the Oeningen insect 

 fauna which the number of individuals will furnish. This is indicated by 

 the following table: 



It will be seen that in all the orders that are well represented the pro- 

 portion of specimens of each is very different, with the sole exception of 

 the Hemiptera, while the same groups (Orthoptera, Arachnida, and Lepi- 

 doptera) are feebly represented in both. The greatest difference occurs in 

 the Diptera, which are less than 7 per cent, of the whole at Oeningen and 

 about 30 per cent, at Florissant; in the Hymenoptera, which have less than 

 14 per cent, at Oeuingeu and 40 per cent, at Florissant, due largely to the 



