240 Address, before the Association of American Geologists 
as described by Prof. Emmons, is one of the most interesting. 
The same gentleman has, also, given us some remarkable details 
respecting the occurrence of genuine injected veins of limestone 
in granite, in the county of St. Lawrence. The facts have led 
him to discuss the question whether all primary limestones ought 
not to be classed among the unstratified rocks. This question, I 
apprehend, we have in this country abundant means of deciding, 
as we have the analogous question respecting serpentine; since 
we have numerous and extensive beds of both these rocks:associ- 
ated with the oldest of our strata.. That they are. metamorphic 
in a high degree, no one can doubt: nor is it less certain that 
serpentine connected with talcose. slate and gneiss, exhibits nu- 
merous divisional planes; and often these are parallel to the 
_ Planes of stratification in the adjoining. strata ;—but the question 
still remains, whether: that divisional structure may not be. the 
result.of metamorphic agency instead of original deposition. 
The northwestern border of the primary stratified belt of rocks, 
extending from Alabama to Canada, a distance of at least twelve 
hundred miles, is composed of interstratified beds of taleose and 
mica slates, gneiss, and granular limestone... I do not doubt (at 
least, from all that I can learn) that these rocks are continuous over 
this vast distance ; forming perhaps the longest belt of limestone 
on the globe. A comsidongbla part of this limestone is more oF 
less magnesian ; and in many places pure dolomite. | It furnishes; 
therefore, a fine field for studying the phenomena and the origi 
of dolomitization. . As to that portion of this field which has fall- 
en under may. observation, I find, that with one or two unimpot- 
tant exceptions, all the cases of dolomitized limestone ocett; 
either in the vicinity, of a fault, or of unstratified rocks, or of the 
oldest gneiss. The pure dolomite is usually found where there is 
reason to believe extensive dislocations of the strata occur; and 
fic marks of stratification in the limestone disappear, nearly 
proportion to the amount of magnesia which it contains, so that 
tie dolomite. shows. ienensiaesiey traces tii it. [doubt not 
5 similar conclusions w Xa n 
