\{U\ TluAiniriciiii ( iiiilixjist . Septfiiilier, ISIM 
liar(U'iiiii<i' of oiu' stnitiiiii licfoiv coiiiiiuMiciii^' the deposi- 
tion of anotlu'r. would he solely speculative. I have not sufficient 
data from my own or.others" observations of volcanoes as to the 
average (piantity of matter annualh' washed down from their 
sides, either hy ordinary rains or durintr seasons of extraordi- 
nary floods, to make from the annual erosion an estimate of time 
necessary to form such deposits as the cono;lomerate strata 
beneath the city of ]M:iii:i<xua and exteiidin>i' towani the extinct 
volcano Masaya. 
There certainly has been an epoch of great elevation and jilaci- 
ation in part of Nicaragua, and a subsequent epoch of subsidence 
in all, and much ice melting and torrential floods in parts. There 
are many evidences here of the occurrence of the Glacial. Cham- 
plain and Terrace epochs. Prol)aV)ly this stratum containing 
human footprints, and the superimposed strata, were deposited 
during the later elevation and depression of the Champlain epoch 
and early part of the Terrace epoch: if so, then there is in Nicar- 
agua evidence of men in large numl>ers and congregated in large 
towns or cities of thirty thousand or more, during the later Cham- 
plain or early Terrace epoch. And. if we accept M. Forefs 
calculations in reference to the time occupied in silting parts of lake 
Geneva by the river Rhone in an effort to get at the date of the 
conclusion of the glacial period there, as a basis for the hardening 
of the stratum underneath the citv of Managua, we can probably 
say more than fifty thousand years ago. 
yUiniupid. X'n-drtiijiui. Xnv. 10. 1890. 
THE POST-ARCH/EAN AGE OF THE WHITE LIME- 
STONES OF SUSSEX CO., N. J.* 
A KEPLY TO A REVIEW t 
Fi!.<iNK I-. N.\siiN, Jefferson Cit.v, Mo. 
In the review of the above paper the writer feels that Prof. 
Dana has laid undue stress upon some of the evidence adduced in 
support of his views and not enough on other. 
It does not seem to l)e logical to aSsume. l)ecause a limestone 
contains chondrodi,te. magnetite and the oxides and silicates of 
zinc, together with intruded granite, that no amount of evidence 
*Ann. Hep. State Geologist of N. J., 1890. 
tNotice of Anil. Rep. State Geologist of N. .T., IStKt, .T>ilv Number of Am. 
.Tour. Sci., 181(1 ;.T. D. D. 
