530 PRINCIPLES OF STRATIGRAPHY 



finest lime-mud, accumulate in shallow water or in part even above 

 the normal level of the sea. In form they probably constitute a 

 sort of mud flat delta, the mud being brought and spread out in 

 part at least by streams, which must have derived it from the 

 erosion of earlier limestones. Mud cracks or desiccation fissures 

 testify to the shallow water in which these sediments were accumu- 

 lating. On exposure partial hardening permits the formation of a 

 superficial crust, which may subsequently break or become de- 

 formed by the sliding of the entire mass seaward. Such sliding has 

 been observed in modern deposits as discussed more fully in Chap- 

 ter XX. 



Fracturing and Piling Up of Material. If the surface layers 

 alone slide, a fracturing will result which produces a mass of 

 angular or subrounded flat mud-cakes, which will be piled together, 

 as the result of this sliding, in a confused mass, the fragments most 

 frequently standing on end, but also inclined in all directions. They 

 will be surrounded by the fine still fluid mud which wells up around 

 them and in which these fragments become embedded. Thus is 

 formed an "edgewise conglomerate," as these accumulations have 

 come to be known, a contemporaneous feature abounding in the 

 finer calcilutytes and calcarenytes of all horizons. Both the cakes 

 and the enclosing matrix may contain organic remains ; the former 

 would carry such fine organic fragments as sponge spicules, plant 

 fibers, etc., which may be washed in with the mud or may exist 

 in the water in which it is deposited, while the matrix becomes 

 normally fossil-bearing since it is a part of the submerged deposits. 

 Professor Seeley (24) (Brown-i) has considered the cakes, as a 

 whole, due to organic growth, and described them under several 

 species of the new genus Wingia. The intra formational conglom- 

 erates described by Walcott (31), though mostly of a much coarser 

 character, probably in part represent such gliding conglomerates. 

 Examples where such cakes of lime-mud carrying fossils were 

 formed through fracturing on drying have been described by Hyde 

 (16) from the Coal Measure limestones of Ohio. In these cases, 

 however, no sliding seems to have occurred, the fragments being 

 embedded where formed. These "desiccation conglomerates" will 

 be referred to again in Chapter XX. 



Distortion of Layers in Gliding. If a large mass of rock slides 

 there will be less of fracturing and more of distortion of the layers 

 along the gliding zone and this will be pronounced in proportion to 

 the weight and compactness of the beds overlying the gliding plane. 

 Good examples of such distortion are found in the Trenton lime- 

 stone of New York (Hahn-12) as exposed in the gorge at Trenton 



