Campbell — Fractured Bowlders in Conglomerate. 233 



faulted, but in other places the movement has been gentle and 

 the rocks dip lightly toward the center of the field. 



At a point on the north side of the basin on the old Indian 

 trail across Mescal Mountain to San Carlos, the bed of bowldery 

 conglomerate dips toward the south or center of the basin 

 at an angle of less than 10 degrees. The soft matrix of tuff 

 has been dissolved and the bowlders are scattered over the 

 ground in great profusion. At this place the specimens shown 

 in figure 2 were found. They were not in position, but their 

 original relations are apparent. 



Almost every bowlder of the thousands scattered over the 

 ground at this place is marked by one or more bruises where 

 other bowlders have been pressed against it. Considerable 

 movement is indicated by these bruises, for the surface is 



Fractured bowlders from coarse Cretaceous conglomerate. Pinal County, 

 Arizona. Scale, one-half natural size. 



ground and crushed in a way that could only occur under 

 repeated crushing strains. In some instances the opposing 

 bowlder has failed to make an impression, probably because it 

 was composed of softer rock, or because some more resistant 

 bowlder took the strain, relieving the pressure in the surround- 

 ing material. The large bowlder shown in the cut has at least 

 six bruises, the two most severe being the one on the front 

 and the one at the left end seen in profile. At these two 

 points the opposing bowlders have been forced into this one 

 until it has been nearly broken to pieces. Great cracks have 

 opened in various directions and the broken parts have been 

 thrust out until it appears like a ball of partly hardened clay 

 that has been squeezed from several directions. The other 



