IN THE DEGRADATION OF THE LITHOSPHERE. 365 



under geological conditions. Even unconsolidated sands show this 

 same disposition under the atmosphere to arrange themselves in the 

 repeating patterns which are so common in the case of rock masses 

 undergoing disintegration under the influence of the atmosphere. 

 One of the illustrations of this I wish to show is from the behavior 

 of the loose sands which overlie the Talbot formation along the 

 Delaware Coast (Figs. 1-2. Plate VI). These sands are disin- 

 tegrating and falling in a series of parallel lines which are surpris- 

 ingly like the joint control of weathering in such a place as the Grand 

 Canyon of the Colorado and indeed in many mountain and other ele- 

 vated rock structures. This parallelism show'n even in these loose 

 sands seems to appear in practically all types of rock structure and 

 would seem to be part of the essential character of rock masses them- 

 selves, though I do not in this case, of course, mean that these sands 

 are to be regarded as jointed ; I do mean, however, that the shape of 

 the sand under disintegration is something which is due to the nature 

 of the sand itself and is not atmospheric in its original cause. 



The literature regarding joints and jointing structures is now 

 large and w^idespread. It need not be reviewed in detail here as it 

 is general principles that I wish to discuss, not the details of the 

 literature. However, certain general works may be cited. Earlier 

 discussion will be found in the work of Giinther ;^ also Giinther ;- 

 Leipoldt and Peschel;^ Penck ;* Supan.^ All geologists are doubt- 

 less familiar with the discussions, on earth features including joints 

 in the monumental work of Suess on " The Face of the Earth." 

 Later literature references may be found in papers by W. M. Davis 

 in the publications of the United States Geological Survey, and to 

 his papers in the BnlletUf of the Geological Society of America. 



Those who are interested in the nomenclature of faults and 

 joints may consult the report of the committee" of the Geological 



1 " Lehrbuch d. Geophys.," Stuttgart, 2 vols., 1883. 



2 " Handbuch d. Geophysik," 2 vols., Stuttgart, 1899. 



3 " Physische Erdkunde, etc.," Leipzig, 2 vols., 1879-80. 

 * " Morph. der Erdoberflache," Stuttgart, 2 vols., 1894. 

 ^ Grundziige dcr Phys. Erdkunde, 191 1. 



^' Vol. XXIV., pages 187-216 especially. 



7 Bull. Geol. Soc. Amer., Vol. XXIV., pp. 163-186. 



