44 NEW YORK STATE MUSEUM 
New York is wholly lacking, hut judging by the occurrence in cen- 
tral Pennsylvania of rocks of the same age as the Little Falls 
dolomite, it is highly probable that the Little Falls sea also covered 
western and southern New York. 
The Little Falls dolomite is especially significant in two ways; 
first, because it is the youngest (uppermost) Cambric formation in 
the State, and second, there is a distinct unconformity at its summit. 
By unconformity here we mean that, after the deposition of the 
dolomite, at least all of northern New York was raised (without 
folding or faulting) above sea level and underwent erosion for a 
moderate length of time after which most of the region again set- 
tled below sea level to receive the deposits of later (Ordovicic) age. 
This old eroded surface and unconformity has been well established, 
and hence we learn that the great Cambric period of the early 
Paleozoic era closed with all of northern New York, at least, well 
above sea level. In southeastern New York, so far as known, the 
Cambric strata appear to grade into the Ordovicic and,if so, that 
region was not raised above sea level at the close of the Cambric. 
We are wholly ignorant as to the physical geography of western 
and southern New York at the close of the Cambric because the 
records there are not accessible, as they are deeply buried. 
ORDOVICIC PERIOD 
We are now ready to consider the physical condition of the State 
during the great Ordovicic period of earth history. During this 
time the Appalachian mountain region, the great Mississippi valley, 
and much of the far western region were almost continually under 
water (see figure 16). In fact, the very widespread distribution of 
thick Ordovicic strata shows that more of North America was 
covered by the Ordovicic sea than by any other sea, with the pos- 
sible exception of the Precambric. Among the more prominent 
lands which persisted above water were Appalachia, a great land 
mass occupying what is now the Atlantic sea board and extending 
an unknown distance into the Atlantic, and another large land area 
in the Hudson Bay region of Canada. Sediments from those lands 
were washed into the Ordovicic sea which, for most part at least, 
covered the State during the entire period. In eastern and south- 
eastern New York, the almost unbroken succession of Ordovicic 
strata shows that the sea was much of the time present there 
during the entire period. The prominent development of Ordovicic 
strata west and south of New York makes it practically certain 
