THE FLORISSANT LAKE BASIN. 35 



or ii somewhat wamier climate. If" we inquire what testiuioii}' tlie lower 

 orders of Florissant insects bear to the climate of that district in Tertiary 

 times, there is only one answer to be given: the present distribution of 

 their allies certainly points to a considerably warmer climate than now — a 

 climate which may, perhaps, best be compared to the middle zone of our 

 Southern States. The known living species of the genera to which they 

 belong are in general credited to regions like Georgia in this country and 

 the two shores of the Mediterranean in Elurope, or even more southern 

 districts. Further remarks on this point will be found in the body of the 

 volume. 



As noted above, the superabundance of specimens of single species of 

 plants (Planera and Myrica) is repeated in the insects, where certain spe- 

 cies of Formicidaj among Hymenoptera, of Bibionida? among Diptera, of 

 Cercopida and of Alvdina among Hemiptera, are to be counted by fifties 

 and hundreds. 



The only other general feature which may already be noted among 

 the insects is an unexpected paucity of aquatic larvae or the imagos of 

 water-insects. Hardly a dozen neuropterous larvge have come to hand, 

 very few aquatic Hemiptera in any stage, and of HydrophilidjE and other 

 water beetles no great number. The paucity of neuropterous larvae is the 

 more remarkable from the abundance of Phryganida;, while not a single 

 larva-case has been found. 



As to the age of these deposits, the opinions of Lesquereux, based on 

 the study of .Tertiary plants, and of Cope, drawn from his knowledge of 

 Tertiary fishes, are far more harmonious than one would expect from their 

 known divergence of view concerning the testimony of the fossils to the 

 age of other Tertiary beds in the West. Such disparity of ideas did hold at 

 first, Mr. Lesquereux maintaining in his earlier notices of the flora the 

 probability of its later Miocene age ; in the Tertiary Flora he placed it in 

 the " Upper Green River" division T)f his "fourth group," together with the 

 flora of P^lko, Nevada, the Green River beds being placed directly beneath 

 them. In Hayden's report for 1876 he refers the Florissant deposits lo the 

 u[)per Miocene. In his review of Saporta's Monde des Plantes,' while still 

 considering this flora as Miocene, he points out certain important relations 

 which it bears to the flora of Aix, in Provence, then considered as Eocene. 



' Amer. Jour. Sci., sev. :!, vol. 17, l5i79, p. 2'9. 



