4 GLACIAL AND SUEFACE GEOLOGY OF THE PACIFIC COAST. 



In endeavoring to give as clear an idea as possible of the character of the 

 geological work Avhich ice is now doing in various parts of the world, the use 

 of some technical terms will be necessary. Most of those commonly em- 

 ployed in the text-books are, no doubt, familiar to the reader; but for a 

 more precise understanding of the discussion which follows, it will be desir- 

 able to define and limit the use of certain terms of frequent occurrence, so 

 that these may be employed without any danger of their use leading to 

 erroneous ideas. The language is, it is true, deficient in words required 

 to express what is often needed to be said in such a way as to include no 

 theoretical views. Even with the aid of Latin words, the difficulty has not 

 been entirely gotten over. 



The simple word " gravel " has been employed in the gravel volume for 

 the mixture of rounded pebbles and boulders with finer water-worn mate- 

 rials, with which the surface and hydraulic miner has to operate. As used 

 throughout that work, it is of the natiu-e of a miner's technical term, any 

 unconsolidated detrital material washed for gold being called " gravel," while 

 the more or less consolidated is usually distinguished as " cement." In the 

 present volume the term " gravel " will be used with its ordinary significa- 

 tion, as meaning a mass of miconsolidated detrital material, made up chiefly 

 of moderate-sized rounded and water-worn fragments of rock, which uuvy be 

 more or less mixed with sand, and according to its condition may be called 

 coarse or fine gravel, sandy gravel, etc. 



The term " diluvium,*' formerly much used for the superficial detrital 

 deposits, has pretty much gone out of use, and been replaced by " drift." 

 When, however, it is intended in the course of this chapter to refer to 

 " drift," without any limiting of the meaning, or implication that it has been 

 transported from any distance, the word " detritus " will be used, with the 

 corresj)ouding adjective "detrital." By detritus is imderstood any uncon- 

 solidated deposit of fragmental material, be the same coarse or fine, homo- 

 geneous or non-homogeneous, water-worn or angular, brought from a distance 

 or derived from rocks close at hand. By the term "drift" will be designated 

 such detrital deposits as have been moved to some distance from their 

 original place of occurrence ; and by " northern drift " is meant the detrital 

 deposits of Northeastern America, which have been carried in a more or less 

 southerly direction over a large area of country. The term " moraine " will 

 be applied to such deposits as are known by their character and position to 

 havo been left in their present position by glaciers. Most if not all of the 



