360 PROCEEDINGS OP THE AMERICAN LCADEMY. 



Monogr. !•• 0. S. ( ■• s -. 193). Beds of cross-bedded gravel and Band, 



iciated with sandy loam, occur between :i lower and :i higher marl In 



the Lahontan basin : of these Russell says: "the remarkable similarity 



the middle member of the Lahontan Bection, us exposed in certain 



localities, to the . . . deposit formed by meandering streams, lead- u 

 refer its with considerable confidence to similar causes " i Afonogr. 



XI.. I'. S. (.. S., 129). Indeed the whole theory of the variation- of 

 Quaternary climate in the Great Basin depends on a Bubaerial origiu 

 of certain gravel and -and deposits which are in many ways similar to 

 deposits thai have hern repeatedly described as lacustrine in account- of 

 Tertiary formations. 



8. Continental Deposits. — It was during a western excursion with 

 Professor Penck of Vienna in the Buinmer of 1897 thai a possible or 

 probable non-lacustrine origin of many of our western fresh-wa 

 Tertiaries was first clearly presented to me. Since then, I have hud 

 opportunity of seeing something of th fluviatile plain ofthePo, and 

 of recalling what I had long before seen of similar plains in California 

 and in northern India, as well as of reviewing several essays thai bear 

 on the genera] problem here considered ; and the problem has thus come 

 to have an importance that warrants the present review and summary. 



Penck's views on this subject may be found in his " Morphologic der 

 Erdoberflache " (ii, 2 1-36), where he discusses the occurrence ol deposits 

 formed on subaerial plains in the older geological systems. Recognizing 

 thai non-marine formations may result under the action of Various sub- 

 aerial agents as well as within lakes, he suggests the name, continental, 

 to im-lude till such formations, leaving the discrimination of particular 

 deposits to further study. Penck's term deserves acceptance among 

 geologists, as an aid in the general consideration that it set m- desirable 

 to give to the problem of our western Tertiaries ; they might he called 

 "continental" in order to avoid implication of either lacustrine or 

 fluviatile origin. Yet as far as the published descriptions of tl 

 deposits afford evidence of their detailed structure, it appear- to me 

 probable that streams and rivers have had more than lakes or winds to 



do with their formation, and he that "fluviatile" might often to 



advantage replace "lacustrine" in describing them. 



9. Wluviatile Deposits. — It i- perhaps 1 ause so much has been 



written regarding the erosive power of rivers that their constructive 

 powers have been too little considered; bul their capacity to aggrade a 

 sinking area deserves as careful examination as their capacity to degrade 

 a rising area. When acting as aggrading agents, they spread out broad 



