PREFACE. XIII 



the eruptive rocks of the Eureka Distriit, appears as au appendix to this 

 report. It presents the results of a careful examination of several hundred 

 thin sections prepai-ed from a large number of rocks, representing every 

 variet}' known to occur in the I'egion. It is a concise statement of results of 

 a systematic study of the material and is of great interest, bearing directly 

 upon many geological questions connected with eruptive masses. Mr. 

 Itldings's repoi't is illustrated by six plates, fom* of which are reproductions 

 of photomicrographs, showing some interesting featm-es in structure of tine 

 groundmass, and two of di-awings of minute crystals and microscopic objects 

 found in the rocks. At the time these photomicrographs were produced 

 they were superior to auythiug which had been done in this class of illus- 

 tration. 



Mr. Walcott's report upon the ''Paleontology of the Em"eka District" 

 was published as Monograph VIII of the U. S. Geological Survey, in 1884. 

 It gives the results of a detailed study of the organic forms obtained 

 throughout a wide range of geological formations, the region having proved 

 an exceptionally rich one in paleontological material from Cambrian, Devo- 

 nian and Carboniferous rocks. In addition to the descriptions of many 

 forms new to science and the identification of t)ver five hundi'ed species, 

 the report contains notes, more or less full, up<ju many species which 

 presented in their characters or geographical distribution information not 

 heretofore published. The work is illustrated by over five hundred and fifty 

 accurate dra^vings of fossils, arranged on twenty-four plates. Four plates 

 represent the fauna of the Cambrian, two that of the Silurian, ten that of 

 the Devonian, and eight that of the Carboniferous. All specific identifica- 

 tions of organic forms from Eureka referred to in this \\()rk wen- made 

 by Mr. Walcott. 



After the completion of the field work for the pAireka map, .Mr. J. S. 

 Curtis began his investigations of the ore deposits found on Kub^- Hill. 

 The surface maps published by Mr. Curtis were taken from the atlas sheets 

 accompanying this monograph. Mr. Curtis's report appeared in 1884 as 

 Monograph VII of the U. S. Geological Survey, and is entitled "Silver-Lead 

 Deposits of Ein-eka, Nevada." It is a valuable work and one which forms 

 an impoi-tant part t»f the scientific memoirs relating to tlic Eureka District. 



