Geology and Mineralogy. 476^ 



5. Formations of eolian origin, as sand-dunes. 



6. Formations in swamps and marshes, as peat-bogs. 



7. Formations in deltas, which are in part fluviatile and in 

 part marine or lacustrine. . 



8. Formations of glacial origin. 



9. Formations usually designated as Loess, which by some 

 have been considered eolian ; but later investigations seem to show 

 that Loess is formed in part, at least, of glacier-ground rock- 

 flour deposited in quiet waters. 



10. Formations called soils and sub-soils, which cover the 

 greater part of the surface of the land. 



The Quaternary formations have proved to be of prime impor- 

 tance, because the principles of geology derived from their in- 

 vestigation constitute a large body of the doctrines applied in 

 the study of the older formations. The rocks are also of great 

 interest, and have been and will be studied in great detail, be- 

 cause of their industrial importance, and because, being at the 

 surface, they are open to view, and ever present questions of in- 

 terest even to the passing observer. 



These formations represent a period or constitute a system in 

 the proper sense of that term ; and the period is distinguished 

 from all others because the formations are classified on a distinct 

 basis, because they overlie all other formations and cover the en- 

 tire extent of lands, and because the general principles of geol- 

 ogy are mainly derived from their study. 



All of the great genetic classes which have been mentioned, 

 except, perhaps, the Loess, have been divided into subordinate 

 parts, for each one of which some conventional sign is necessary 

 in the preparation of Quaternary charts. It will thus be seen that 

 a special system is necessary for their representation. 



Yet another fact must be considered in this connection. The 

 Quaternary formations cover, to a greater or less extent, all other 

 formations ; and the chart designed to represent the distribution 

 of older formations cannot be used to represent the Quaternary 

 formations without imposing one system of conventional symbols 

 upon another. The attempts to do this have not been generally 

 successful, and it has been and will be found that special Quater- 

 nary maps are necessary, and a system of cartographic conven- 

 tions must be devised for this purpose also. 



The conclusions reached in the foregoing statements are as 

 follows : 



1. The Quaternary or Pleistocene formations represent a dis- 

 tinct period or system. 



2. The Quaternary period should be defined as beginning with 

 the glacial epoch. 



3. The Quaternary formations are fundamentally classified by 

 agency and condition of origin. 



4. A cartographic scheme is necessary for the representation 

 of Quaternary formations. ■ 



