50 



S. R. CAPPS 



curved surfaces on their other sides. At one place a steep 

 overhanging sea cHff 30 feet high was formed by the base of such 

 a flow, the underlying slate having been cut away. The base of 

 this flow was flat and smooth, though the flow, as seen in section, 

 was composed altogether of ellipsoidal lavas. Into the cracks in 

 the base of this flow the mud had penetrated deeply. It is believed 

 that the flat lower surface of this ellipsoidal flow could have been 



Fig. 5. — Ellipsoidal lavas below, separated from more massive diabase above by 

 an intercalated shale bed. The lower surface of the shale is uneven, having taken the 

 shape of the ellipsoidal lava surface upon which it was deposited. The overlying flow 

 is flat on the bottom, conforming to the shale surface. Photo, by S. Paige. 



formed only by lava which was poured out upon a flat bed of sedi- 

 ments, the lava having conformed to the surface upon which it 

 was deposited. The upper surface of an ellipsoidal bed presents a 

 different appearance (Figs. 4 and 5). There the flow surface was 

 under the pressure only of the column of water above it, and 

 the surface hardened to form an irregular floor consisting of a 

 succession of domes, like the surface of a magnified cobblestone 

 pavement, the surface of the ellipsoids representing the cobble- 



