SHALLOWNESS OF THE MESOZOIC SEA. 
213 
difficult to understand how so vast a mass of strata could have accumulated 
in such shallow waters and over so wide an area. And the difficulty be- 
comes considerably greater when we recall the fact that coal was also 
accumulated at different horizons throughout the entire province If the 
sea were everywhere so shallow and if notable portions of its area were 
raised above the surface sufficiently to permit the growth of land vegeta- 
tion, it would seem difficult to account for the transportation and diffusion 
of so large a mass of sedimentary materials over the entire expanse. Pos- 
sibly some of the difficulties will be lightened by the following suggestions 
Although to the eye the strata show no marked inclinations excepting 
such as we know have been produced in later periods, still there may have 
been, and probably were, very feeble slopes too small to be detected by the 
eye, and these feeble slopes if continued for any great distance would carry 
the surface down hundreds of feet. A slope of one degree means a differ- 
ence of level of a thousand feet in less than eleven miles. Hence there is 
no difficulty in imagining that while some tracts were exposed just above 
the water level, there were still larger ones where there may have been more 
than a hundred fathoms of water. But it should seem that shallow water, 
provided the shallowness be not very extreme, would tend to a wider and 
more uniform distribution of sediments than waters which run off into great 
depths. The currents having less depth of cross-section would move more 
rapidly and constantly, while currents moving outward into deeper water lose 
velocity and transporting power. So fai’, then, is the shallowness of the 
Plateau sea from being an obstacle to our comprehension of the state of 
facts which the region presents, that it may be the key to the mystery. One 
of the most striking facts to be explained is the persistency of lithological 
characters over large areas and the very slight and gradual variations in the 
masses of strata from place to place. If these sediments had been brought 
down by rivers to a shore from which the waters steadily and rather rapidly 
deepened seawards, we might have looked for enormous masses of littoral 
beds which rapidly thinned out as they receded from the shores ; for the 
moving currents might be expected to lose themselves in the deepening 
water. But with shallow waters, whatsoever currents might be generated — 
whether from tides, from large rivers, from oceanic drift, or from prevailing 
