- 
teristic features. The limits of the ocean admitting of rock de- 
position at this period never extended so far north by many 
miles as in the period of the Burlington limestone. 
The Warsaw Archimedes limestone appears to have been 
nearly coextensive with that below, so far as known at present. 
The St. Louis limestone extends northward also, nearly or quite 
to the same limit, but only in a thin brecciated or conglomeratic 
mass which has been rarely recognized above the lower rapids 
of the Mississippi. It is only on descending the valley to the 
neighborhood of Alton that this rock appears in any considera- 
ble force. 
To these limestones succeeds the sedimentary deposit of ferru- 
ginous sandstone, which in the river valley is not known far to 
the north of St. Louis, while the succeeding Kaskaskia limestone 
becomes important in the vicinity of the Kaskaskia river, and 
is known in the interior as far north as Prairie de Long, and in- 
creases in force as we go southward. 
We have most clearly therefore the evidence that the limits of 
the ocean admitting of calcareous deposits was gradually con- 
tracting, at least in the direction from north to south, leaving the 
more southern portions as the areas of greatest development for 
these limestones. 
Some interesting inquiries are suggested by these facts, and 
at the same time they afford in some degree the solution of a 
difficulty which has heretofore been unexplained. 
It is well known that no limestone of the age of those here 
described, occurs beneath the coal measures on the western side 
of the Appalachian coal field north of the Ohio river; nor upon 
the eastern side of the same field, till we reach the central part 
of Virginia. The same is true of the coal fields of Nova Scotia 
and New Brunswick according to Prof. Dawson, the northern 
sides exhibiting no underlying limestones, while these rocks do 
appear coming out from beneath the coal measures on the one 
“4 : 
unconformable, differing only in degree. 
It would spree, that at a period long preceding the max? 
mencement of the carboniferous limestone deposits, the ance? 
Ocean began to contract its area; that this contraction was due t 
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