Peneplains of the Ozark Highland. — Hershey. 41 
iographic development of the Ozark highland, may be briefly 
summarized as follows : 
1. The entire region was reduced by subaerial erosion to 
base-level, forming the Cretaceous peneplain. 
2. A great dome-shaped uplift was instituted over the 
j-ite of the southern two-thirds of the present Ozark highland. 
The amount of elevation was 1,200 to 1,500 feet in west-cen 
tral Arkansas, 500 feet in the Boston mountain region, 100 
feet along the IMissouri-Arkansas line near Eureka Springs, 
and nothing from the "crest of the Ozarks" north. The long 
Tertiary cycle of erosion again base-leveled this region, form- 
ing the main Tertiary or "Tennesseean" peneplain, except that 
residuals were left in the Ouachita and Boston mountains. 
3. An uplift, general throughout the Ozarks, of seventy- 
five to one hundred feet, increasing to 300 feet in the White 
River country, enabled a Pliocene cycle of erosion to excavare 
the broad basin valleys and reduce much of the country to a 
new base-level. The close of this cycle of erosion was con- 
temporaneous with the end of deposition of the Lafayette for- 
mation in the ^Mississippi embayment region. 
4. Another general uplift, insignificant in amount south 
of the Arkansas river, but increasing to a maximum of at least 
several hundred feet in southern Missouri, enabled the streams 
to excavate the canyon valleys of Ozarkian age. 
5. An undoubted local uplift of the Boston mountains 
and contiguous areas in the ^Modern epoch. As most of the 
Ozark highland is far above a base-level, it may be presumed 
that the late Quaternary elevation has been quite general, but 
has occurred so recently, geologically speaking, that only in a 
few limited areas are its effects as yet noticeable. 
Nov. 15. 1899. 
CORRESPONDENCE. 
Troost's Survey of Philadelphia. Apropos of Dr. Merrill's in- 
teresting communication in the December number of this journal I 
beg to call attention to the fact that, safely housed in the library of 
the Academy of Science of Philadelphia along with other bibliograph- 
ical treasure?, is a copy of Dr. Gerard Troost's Survey of the environs 
