STUDIES FOR STUDENTS 185 



Overlying beds are undeformed or share only in later deforma- 

 tions affecting the entire body of the strata. Their contact is 

 accordant where the breccia has been reworked and leveled by 

 wave-action. In this case they contain at bottom fragments of the 

 broken beds, either rounded to a conglomerate or partially angular 

 and forming a pudding or rubble breccia. If the slidden mass is 

 reassembled below wave-base the contact is discordant and super- 

 incumbent beds are free from fragments. The breccia may thus 

 be either endostratic or have the hummocky upper surface of a 

 landslide. Glide breccias may graduate laterally as well as verti- 

 cally into sedimentary beds. They rest on undisturbed strata of 

 earlier date. Endostratic breccias passing within the limits of the 

 same stratum into folded laminae point strongly to an origin in 

 glide. A complete section of a glide and the associated strata 

 would show, according to Heim, 1 the following relations: in the 

 area bared by the glide, (1) a reduction of the number of strata as 

 compared with the adjacent areas, (2) local disconformity with- 

 out time interval; in the area on which the glided mass came to 

 rest, (3) increase in the number of strata, (4) superposition of older 

 on younger beds, (5) displacement of facies. Glides involving 

 subaqueous and subaerial sediments have occurred in a number of 

 instances on the shores of the Swiss lakes, in Sweden, and along 

 the Black Sea. 2 In the lower Devonian limestones of Gaspe a bed 

 has been described by Logan 3 whose structure is evidently due to 

 subaqueous glide. This bed, 7 feet thick, is made up of several 

 thin layers of limestone and limy shale, wrinkled, contorted, and in 

 places breccia ted, while the associated beds are free from marks 

 of deformation. 



The edgewise position of broad, flat pebbles in evenly bedded 

 strata near Bellefonte, Pennsylvania,* has been attributed by 

 Brown 4 to subaqueous glide. 



Endolithic breccias. — Of breccias formed within the lithosphere 

 the following classes may be distinguished: (1) tectonic breccia 

 (dynamic, pressure, friction breccia), due to crustal movements 



1 Quoted by A. W. Grabau, Principles of Stratigraphy (New York, 1913), p. 660. 



2 Grabau, op. oil., pp. 657 f., 779 f. 



3 Sir W. Logan, Geology of Canada (1863), pp. 391 f. 



4 T. C. Brown, Jour. Geol., XXI, 241-42. 



