EMBANKMENTS AT BUFFALO SPRINGS. 117 



Reaches took place during' the last high-water stage of the lake. This de- 

 lerraination, however, will appear more clear to the reader as we advance 

 with our studies. 



An inspection of the map shows that all the structures there repre- 

 iented were built in a rising lake, and were but little, if at all, modified by 

 the waves and currents as the waters receded. This statement requires 

 qualification however. We may be certain from the perfection of the ridges 

 chat the retiring waters did not tend to destroy them, but, on the other hand, 

 they may have received additions. It is probable that gravel structures 

 like those under discussion, when formed in a rising lake, would induce dep- 

 osition at the same horizons during a recession of the waters. The sec- 

 tions of the structures at Buifalo Springs fail to give information on this 

 point. 



The only modifications that have taken place in these deposits in post- 

 Lahontan times are due to the erosion of the rills that cross them and the 

 partial removal of the fine sediment deposited over the older bars. 



At the extreme distal end of the embankment that projects into the 

 valley there are considerable accumulations of sand, illustrating the fact 

 that fine material is carried farthest by currents when structures of this char- 

 acter are found, andshowing why the bottoms of gravel embankments are fre- 

 quently composed of sand. On either slope of the embankment the gravel of 

 which it is composed is concealed beneath fine sediments, which must have 

 been deposited when the lake stood over the structure. The looped bars 

 high in the series at one time contained lagoons in which mollusks found a 

 congenial habitat, as is shown by the multitudes of shells, principally of 

 Pompholyx, that crowd the marls in the miniature playas behind a num- 

 ber of the embankments. 



Three miles south of Buffalo Springs there is another group of embank- 

 ments similar to that described above. These are represented on the sketch- 

 map forming Plate XXI.*® 



*'Tliis map is lessaccvirate tban the one forming Plate XX, bat it indicates the main features of the 

 structures as well as eoulcl be desired. The figures ou Plate XXI are from aneroid measurenient.s, and 

 indicate apijroximately the depth of water at the highest water stage of Lake Lahontan. The figures 

 on Plate XX are from measurements with an engineer's level, and may be considered accurate. 



