ON THE GEOLOGY OF THE UNITED STATES. 
61 
across the Rhone, to the Mediterranean ; the limestone_, during 
this long course, is similar both in colour and structui'e, and in 
some places on the banks of the Danube, is in a schistose form. 
The absence of the newest floetz-trap formation (which par- 
tially and irregularly covers all other formations, thereby break- 
ing the continuity of the strata), as well as the effect of the vio- 
lent convulsions and earthquakes so frequent in the vicinity of 
this disputed formation, may be one cause why the prosecution 
of geological research is so much more easy in North America 
than in Europe. A second cause, producing much more univer- 
sal and extensive effects, may perhaps be found in the difference 
of the number and magnitude of the accidents and changes that 
have been effected in the stratification of the various classes of 
rocks on the European continent, since their original formation, 
by the effects of water washing away the more perishable'super- 
incumbent strata, and leaving the more hard and durable parts 
of the same stratifications in their original positions, or by the 
long and continual action of rivers, wearing deep beds, and ex- 
posing to view the subordinate strata, giving to the whole the 
present appearance of confused and interrupted masses, though 
they might have been extremely regular in their original 
state. 
A third cause of the facility of geological investigation in 
North America, may arise from the whole continent east of the 
Mississippi, following the arrangement of one great chain of 
mountains; a fact which, simple in itself, bears out the real 
utility of studying the physical in its relation to the geological 
structure of any district, and as affording evidence of a rule, very 
general in its application, and very little liable to exceptions. 
This chain of mountains, the axis, we may so term it, of the geo- 
logical structure of the United States, commences at the St, 
Lawrence river, and appears to be a spur from the great mass of 
primitive, which occupies all the northern parts of the continent^ 
runs in a south-westerly direction to the borders of Florida, is 
