

with Observations o?i the study of Terraces. 13 



extending as they do throughout the interior of a whole country, 

 are marine. It will be time enough to speculate on the facts, 

 when they are ascertained. The terraces consist of material of 

 all kinds, from the coarsest pebbles to the finest silt, and assuredly 

 the sea, if the source, must have left some traces of itself and its 

 productions, which may be detected where such extensive de- 

 posits remain undisturbed. 



The writer has observed terraces along the rivers of Oregon 

 and California as well as in the eastern portion of our country, 

 and for some years has been hoping to take up the subject for 

 special study, feeling assured that a phenomenon which so per- 

 vades a continent, as is evident throughout the United States 

 from east to west, must afford conclusions of the highest interest 

 to geology. Mr. Chambers's work contains much valuable ma- 

 terial, showing at least the wide distribution of terraces over 

 his own country, as well as to some extent in other lands. But 

 more study is required before the great body of the facts he has 

 collected are made available to science. The subject should be 

 entered upon in the manner exemplified by that accurate and 

 laborious Scotch geologist, Macculloch,* and carried out with 

 still more minuteness of detail. 



1. The heights of the terraces above the bottom of the river 

 valley on both sides, should be measured by careful leveling, and 

 sections should be thus made through the whole course of a stream 

 from its mouth to its head, at as many places as practicable. 



2. The height of the river above the sea should also be ob- 

 tained for each place, where a section is thus made. 



3. The horizontal ity or slope of the terrace plains along the 

 valley should be determined : and to this end the length of any 

 breaks in a line of terraces, met with on the ascent of a stream, 

 should be noted, and the physical features where such breaks oc- 

 cur, in order to understand the causes of them : also the nature 

 of the river's bottom, upon which fact it often depends whether 

 the terraces may or may not correspond in slope with the exist- 

 ing slope of the stream, and also what may be their height in 

 different places. 



4. The relation should be ascertained, if there be any, between 

 the heights of terraces on the smaller tributaries and those of the 

 main stream, or between the stream where the descent is rapid 

 and where it is nearly horizontal ; also between small and large 

 streams in the same vicinity. 



5. The character of the deposits, whether alluvial, lacustrine, 

 or of beach or sea-coast origin, applying the tests mentioned, 



should be matters of thorough investigation. Assuredly, if no 





marine relics or indications are found along a river's terraces for 

 one or two hundred miles, it would be defying all geological 

 principles to assert that such deposits were marine. 



* See Ueol. Trans., vol. iv, pi. 21- 



