i 913 ] Lawson: Designation of Alluvial Fan Formations 333 



But bold relief is the immediate result of acute diastrophism 

 and this fact must be taken into consideration in the attempt to 

 determine the geological age of the formation. Such disturb- 

 ances occurred at the close of the Carboniferous, and at the close 

 of the Jurassic. The correlatives of the formation doubtless 

 occur in other parts of Nevada where post- Jurassic granite 

 abounds and if in such localities the formation should be found 

 to be devoid of granite fragments a presumption would lie 

 established in favor of a pre-Jurassic age. Whether it be pre- 

 Triassic or post-Triassie can probably be determined by its 

 relations to the Triassic rocks to the west of Battle Mountain. 



The tracing out of the distribution of this fanglomerate will 

 be an interesting contribution to the geology of Nevada since it 

 affords a definite datum of a peculiar kind from which the 

 geological history of the region may be reckoned. It is not only 

 a positive mark in the geological time scale, but a mark which 

 may be interpreted in terms of climate, diastrophism and 

 physiography. 



Scarcity of Fanglomerate among the Books of the Past. — The 

 abundance of fanglomerate now in process of accumulation in 

 the arid regions of North America at the present time suggests 

 that similar rocks should be found among the continental deposits 

 of the past more commonly than the observations recorded in 

 geological literature would indicate. It is posible that such rocks 

 have been described under the name of "breccia." and that this 

 term has been inadequate to discriminate them from other types 

 of fragmental rocks, so that their significance has been over- 

 looked. This may be the case, for example, with the so-called 

 "breccias" and "brecciated conglomerates" of the Newark 

 system. But making due allowance for this possibility it is 

 remarkable that there are so few, if any, descriptions of conti- 

 nental formations that correspond with the alluvial fan deposits 

 of Pleistocene and Recent age so abundant in the western part 

 of the continent. If such rocks existed they could hardly fail of 

 recognition and description ; and the inference seems warranted 

 that, in those portions of the continent with which geologists are 

 particularly familiar, fanglomerate docs not occur. If this be so 

 then one or the other or both of the conditions which determine 



