230 J.D. Dana on the Appalachian and Rocky Mountains 
progress, as the investigations of Hayden have shown, through 
much of the Tertiary perioc 
On the eastern border of the continent, only one epoch of pro- 
found disturbance during the progress of Mesozoic time (or the 
Reptilian age)—has been distinguished: namely, that when the 
Triassico-J urassic Scan underwent displacement, and the 
trap ridges and dykes that are associated with it were formed in 
Nova Scotia, the Sammocout valley, the Palisade region of New 
York and New Jersey, Pennsylv vania, Virginia and North Car- 
olina. This a a epoch of disturbance divides off the pe- 
ensof of “i Triassico-J urassic beds from that of the Cretaceous 
ormati 
At close of the Mesozoic, there was some elevation of the 
continent on this same eastern border, but it was small in amount, 
compared with that on the western. 
e destruction of life closing Mesozoic time was as compre- 
mansive and complete in North America, according to present 
ge, as that closing the Paleozoic. Investigation with 
reference to this point has already extended over so wide a Tre- 
gion, that the fact may be regarded as quite well established. 
The exceptions that we have most reason to look for are those 
of oceanic fishes; for these species might have escaped the de- 
stroying agence y. (whether of climate aoa change of level, or the 
latter alone) which was in action over the continents and alon ong 
the ocean’s shallow borders 
It is, then, evident that in 1 North America the two boldest tran- 
sitions in the course of the Zoic ages correspond with tlfe raising 
of the mountain chains of the two oceanic borders, Thus time 
and geography are brought into direct parallelism. 
tensive metamorphic changes, after those which preced 3 
Upper Silurian, appear to date from the time between the Car- oe 
annaine apa "Triassic periods, either at the beginning or close 
e essential conformability of the Cretaceous and siren. beds ee ae part 0 of 
the Atlantic sr ae borders shows that even aan oy 
in geo his not accompanied everywhere ‘by disturbances Ae ‘ar hos 
and cases of unconformity wees is no object pf Bre closing i 
the Permian beds jet th > 
the wor aoe 
wget os de Lady hag questioned in converwation with the wih ie 
