INTRAFORMATIONAL CONGLOMERATES 785 



Finally, it should be mentioned that in the unconsolidated deposit 

 of the Pleistocenic such deformations occur, though some of them, 

 no doubt, are due to glacial thrust. The deformation of the Ter- 

 tiary beds of Martha's Vineyard may possibly belong to this cate- 

 gory. 



Deformation through gliding may result in complete brecciation 

 of the deformed layers. The fragments may lie in all positions, as 

 in the case of ordinary "intraformational conglomerates." or they 

 may consist of thin cakes, many of which in the gliding process have 

 assumed a vertical position in the mass. This forms the so-called 

 "edgewise conglomerate" common in the Ordovicic limestones of 

 the Appalachian region. The characteristics of all these forma- 

 tions seem to point to rather shallow water as the place of deposi- 

 tion of these strata, and the possible periodic exposure and partial 

 hardening of the surface layers. A different explanation has, how- 

 ever, been given for these by Seely and amplified by Brown (i). 



6. Surface Deformation Due to Creep. As already noted (p. 

 543), vertical strata, especially of a shaly or slaty character, are 

 subject to deformation in portions of their exposed ends by the 

 creep of the surface soil down a sloping hillside composed of thin 

 strata. A bending in the direction of movement is generally found 

 to occur after a while. Such deformation is of slight importance, 

 and is probably never preserved in the older rocks. 



b. Deformations Due to Vertical Pressure of Overlying Rock 



Masses. 



7. Squeezing Out of Layers. This may occur in cases where 

 certain beds are especially susceptible to such deformation. Fine- 

 grained, homogeneous strata seem to be most readily affected in this 

 way. An enterolithic structure similar to that produced by swelling 

 masses (gypsum, salt) is thus produced, the effect being similar 

 whether the pressure originated from the swelling of the mass itself 

 or from the weight of the overlying rock. Koken believes that the 

 enterolithic structure in the Muschelkalk of the Neckar Valley 

 (Gekrosekalke) is due to vertical pressure and squeezing out of 

 these layers. (Ante, Fig. 161.) 



8. Shaliness is the property of lutaceous rocks, rich in clay, to 

 split with concave or "shelly" surfaces in a general way parallel to 

 the bedding ])lanes. The structure is a secondarily derived one, due 

 to vertical pressure and the character of the rock. It seems to be 

 best developed in calcareous shales. That it is a secondary struc- 

 ture is shown by the fact that the splitting will sometimes pass 



