THE GEOLOGICAL HISTORY OF NEW YORK STATE 45 
that the western and southern portions of the State were submerged 
under the Ordovicic sea. In northern New York, however, there 
is no positive evidence whatever that the whole Adirondack area 
was ever completely submerged during this period. Accordingly 
the central Adirondacks formed a persistent island in the Ordovicic 
sea. Furthermore, in northern New York there were various rather 
Fic. 16 Generalized map of North America showing the relations of land 
and water during the Midordovicic period. Horizontally lined areas — land; 
blank areas==water. All of New York State was submerged except 
the central Adirondacks which stood out as an island. The conditions in 
Mexico and Central America are practically unknown. 
local oscillations of level bringing the land around the island now 
above and now below sea level, but all such details are here omitted. 
For our purpose it will suffice to say that, except for the Adirondack 
island, northern New York was mostly below sea level during the 
Ordovicic. To summarize the above statement: New York State 
