208 BAILEY WILLIS . 
brian sea extended further in certain areas than the upper Cambrian 
and retreated while the upper Cambrian sea spread over other regions. 
These details are not well worked out, though in part recognized. 
The map truly presents, however, the general fact that North America 
was to a great extent submerged and the land areas very markedly 
reduced. ‘The prevailingly fine and calcareous sediments of the 
wide seas and the siliceous coastal plain sediments of the littoral 
deposits indicate that the relief of the land was low. 
The conditions of marine circulation had apparently been modified 
by the expansion of the interior sea, and the clmate conditions 
incident to widespread seas and low lands had become so ameliorated 
that similar habitats prevailed throughout a very wide range of 
latitude. 
