HAYDEN'S SURVEY. 511 



regions, the most extraordinary, and as it seems to us impossible, 

 dynamic conditions have been invented, and sections drawn which are 

 not consistent with the theories advanced, nor witli the observations of 

 Professor Geikie, nor with those of the senior author of the present 

 paper. An attempt has been made to divide the granite into eruptive 

 and metamorphic ; and it is claimed that the division thus made in the 

 field was supported by the independent microscopical examination of 

 Professor Zirkel. In point of fact, however, it appears that the latter 

 only observed certain differences between two sets of rocks submitted to 

 him by the geologists of the Fortieth Parallel as having been deter- 

 mined, in the field, to be eruptive and metamorphic. These diftereuces, 

 however, are considered by Dr. Wadsworth to be non-essential, and not 

 such as would, in the case of other specimens from other regions, justify 

 the lithologist in assigning rocks so differentiated to different origins. 

 Indeed, Professor Zirkel, as already staied,* admits this. Furthermore, 

 it appears that at the close of the field-work the crystalline and granitic 

 rocks of the ranges of the Great Basin west of the Wahsatch were con- 

 sidered by Mr. King as being of post-Jurassic age, in accordance with 

 the observations and results of Professor Whitney and his assistants on 

 the Geological Survey of California ; but that some years later, at the 

 time of the publication of the volume of Systematic Geology, these rocks 

 were all classed as Archaean, without any reference to the fact that so 

 radical a change of views on a point of so much ituportance had taken 

 place, and with no sufl&cient evidence for its support. It needs hardly 

 be added, that any reference to a division of the Archaean (Azoic) into 

 sub-groups in the Fortieth Parallel reports can only be looked upon as 

 wholly without importance or value, otherwise than as indicating certain 

 mineralogical resemblances to rocks described as occurring in Canada 

 and elsewhere. 



HAYDEN'S SURVEY. 



In 1868 Dr. F. V. Hayden remarked that the "metamorphic rocks " 

 in the valley of the Chugwater (Wyoming) were probably of Laurentian 

 age, but it is not stated upon what evidence this opinion was founded. 

 (Report of Commissioner of the General Land Oflace, 1868, p. 232 ; 



* See ante, p. 500. 



