ART. XX -THE COLEOPTERA OF THE ALPINE REGIONS OF THE 

 . ROCKY MOUNTAINS. 



By John L. LeConte, M. D. 



The elevated interior region of North America presents peculiarly 

 favorable opportunities for the study of some of the most interesting 

 questions connected with geographical distribution of animals and 

 plants. 



If the materials at our hands be, as indeed they yet are, a very scanty 

 representation of the organic forms now living in that part of the con- 

 tinent, they are, at least, sufficient to indicate the direction in which 

 investigations should be pushed, in order to arrive at definite and final 

 results. 



The peculiarly favorable circumstances to which I chiefly refer at 

 present are dependent on the following points in the development of 

 the region : — 



1st. The gradual enlargement of the land-surface at the expense of 

 the circumambient seas during the latest Mesozoic periods. 



2d. The gradual elevation of the middle of the continental mass dur- 

 ing post-Cretaceous times, so as to greatly modify the climate in respect 

 to both moisture and temperature. These changes have been so gradual, 

 that we may say with certainty (excluding the local eruptive phsenom- 

 ena, which were more numerous, but not remarkably different from those 

 of the present age) there has been no great or paroxysmal disturbance 

 destructive of the land-surface in the elevated plains east of the Eocky 

 Mountains since the deposition of our early Cretaceous strata (Dakota 

 Group). 



3d. While, during the Glacial epoch, the valleys of the mountains 

 were filled with glaciers of moderate size, and the line of permanent ice 

 streams and fields brought to a much lower level, there was an absence 

 of the extensive ice sheets and flooded areas, which in Eastern America 

 destroyed entirely the terrestrial organized beings of the former period. 



It must be inferred from the first and second of these premisses, that 

 the new land exposed by this gradual development of the continent 

 received its colonies of animals and plants from the conterminous older 

 land-surfaces in various directions, and that the subsequent elevation 

 of the continental mass, by which the moisture was diminished, caused 

 a later invasion of the territory by those genera and species which are 

 characteristic of arid regions. 



We may also conclude, from the third premiss, that the glacial displace- 



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