SECTIONS EXPOSED IN HUMBOLDT CANON, 129 



formations; the upper is of a homogeneous, earthy character and has a 

 striking resembhxnce to recent flood-plain deposits. The remarkable sim- 

 ilarity of the middle member of the Lahontan section, as exposed in certain 

 localities, to the bipartite — stream-bed and flood-plain — deposit formed by 

 meandering sti'eams, leads us to refer its oi'igin with considerable confi- 

 dence to similar causes. In some instances the earthy or flood-plain 

 portion of the medial gravels is overlaid by current-bedded debris, which 

 may reasonably be considered as the sheet of shore material spread out by 

 the waves and currents during the rise of the lake that followed the forma- 

 tion of the middle member of the series. 



The accui'acy with which the accompanying detailed sections have 

 been drawn, leaves little room for description; but in order to present 

 still more definitely the facts on which they were based, descriptions of a 

 few of the more instructive exposures ai'e inserted. The lettering of the 

 following sections indicates their position on Plate XXIII: 



.48 



Section A. — West bank of Humboldt Itiver,2 miles south of Oreana. 



Feet. 



1. Jiolian sand and dust, forming surface of the desert- 1 



2. Sand and gravel, massive 3 



3. Loam, sandy, liiminated 2 ^ Uppe laeustral clays 



4. Marly clay, laminated and jointed 



5. Sand and gravel, cross-stratitied 1 



6. Loam and sand, obscurely cross-stratified 5 ^Medial gravels. 



7. Sandy loam, massive ; to river 



16 > 



33 



A double fault-line extends through the series, as shown on Plate XXIII. 

 A similar double fault occurs 300 feet northward of the first, in the same 

 vertical cliff (see Fig. 26, page 165), but the throw is in the opposite direc- 

 tion, showing that the whole included block, 300 feet long, has been bodily 

 depressed 2 or 3 feet. The marly clays forming the upper portion of 

 the section are, as usual, markedly unconformable to the gravels underlying 

 them. 



«In making the drawings of detailed sections represented on Plate XXIII, the entire vertical 

 range of the exposures observed was not represented. 



MoN. XI 9 



