PROCEEDING!^ OF THE NA TIONAL MUSEUM. 



The northeastern region, in the neighborhood of Oclenton, should 

 also be studied more carefully, as, for example, the sand dunes there 

 constitute the only places where the rare Cremastochilus lemostlctuH 

 was found. 



Notwithstanding the attendant difficulties and large extent of unex- 

 plored territory to furnish a nearly complete list of the Coleoptera of 

 the District of Columbia, I must acknowdedge that success is in part 

 due to the encouragement of my friend, E. A. Schwarz, who kindly 

 lent his wide experience and assistance in preparing the annexed 

 biological notes. 



The following important facts have been observed concerning the 

 relation existing between the local geology, flora, and general fauna 

 and the occurrence of the District beetles in special. 



It is a well-known fact that the distribution and varied hal)its of 

 Coleoptera aiford. such striking features that the general physical 

 characteristics of any locality can be determined from an average 

 collection of the beetles of such region. 



The number of species found in the District of Columbia, or, more 

 broadly, in an area within a radius of 20 miles of the Capitol, is not 

 less than 3,000. This is a much larger number than has been recorded 

 from local lists of any other equal area in the United States. It repre- 

 sents about one-fourth of the total number of species now recorded 

 from North America north of the Mexican boundary. 



Let us now examine the physical conditions which form the environ- 

 ment of the Coleoptera here. 



The geology of the District presents the following features: 

 Washington City is chiefly built upon thin beds of sedimentary 

 sands, clays, or gravels of the Post-Jurassic age, covering the Archean 

 crystalline rocks — chiefly gneiss and granite. 



Satisfactory exposures of these rocks are to be found only in the 

 deep ravines cut by the Potomac and Rock Creek or their tributaries, 

 since, at the surface of the Washington plateau, their character has 

 been ol)scured or obliterated by extensive superficial decay and by 

 cultivation. 



Toward the west the gneisses, which are for the most part granitoid 

 in character and possess a north-south strike, become somewhat more 

 foliated and schistose. In many x)laces it appears that the granites 

 and gneisses have been subjected to extensive metamorphism. Near 

 Georgetown and Cabin John occur pronounced developments of a 

 massive dark-green diorite, and in other localities are found bands of 

 siliceous and chloritic schists. These, however, grade imperceptildy 

 into the prevailing granite and gneiss, and probably represent the 

 result of intense dynamic action. Limited occurrences of gabbro, ser- 

 pentine, and steatite complete the list of eruptive rocks found in the 

 District. Altogether they contain at least forty diflerent mineral 

 species. 



