266 ELEMENTARY GEOLOGY 
thinning out in several directions, the strata are usually 
more or less lens-shaped or lenticular (Fig. 150), with 
somewhat indistinct boundaries. Not only do they vary 
in these respects, but some beds are accumulated much 
more rapidly than others; and therefore, in the same 
leneth of time, there may be deposited many feet of 
conglomerate, while the depth of the clay accumulation 
near at hand may amount to only a few inches. 
On the average, the ocean bottom is fairly level, and 
so the layers that are deposited on it are usually nearly 
50 Or ‘s 
O0*9%O Sea ron N . 
° ° ° Re Ese eee peg tthe 
90° 000089095 0206 a2: % 
Fic. 150. 
Diagram to show lenticular form of beds. Vertical exaggerated. Boundary 
lines sharper than natural. 
horizontal, but not always, for there are places where 
the bottom is irregular, and in such, since the layers 
conform to the outline of the ocean floor, they are not 
accumulated in a horizontal position. So sedimentary 
rocks, while generally deposited in horizontal layers, 
may in some cases be formed with the beds tilted at 
a considerable angle. In some parts of the bottom, the 
angle of slope may be as steep as that of the mountain 
side, but such places are exceptional. When built into 
