J. LeConte—Rate of Growth of Corals. 35 
certain level. With the rise of the mean level again, new points 
start upward, to be again clipped at the same level by the de- 
scending water. The levelness, the thick setting, and the dead- 
ness of the points are all thus completely accounted for. It is 
precisely the phenomena of a clipped hedge. 
I have long been accustomed to estimate from these facts 
the rate of madrepore growth. I have recently looked up the 
data necessary to do so more accurately. 
The following table, taken from the Coast Survey Report for 
1853, p. 76, gives the mean sea level for the different months 
of the vear. 
Feet. Dit. Feet. Dif. 
be bo. 10 0 OOF sovese cist “78 ‘68 
‘ ‘ 15 5 OG: iis njiause Od. he 
Margh ~..%- 26 °16 SOph.-su v= dee 93 °83 
April a 26..:36 Oe 90 °80 
ee ge a2 22 INST. oni cols dee is 00 
June oe a ee Ties... a Be ee 
From the differences I have roughly plotted a curve represent- 
ing the annual variation of mean level. 
It is seen that the mean level at Key West is lowest in Jan- 
uary and highest in September, the difference being 0 83 feet or 
about ten inches. Now starting with the lowest mean level in 
January, / /, it is evident 
Pie that living points a@ aa 
sg 8S we dee ; g near that surface would 
a a grow upward and con- 
tinue to grow all the time 
the water was rising from 
litol'l’, i.e, from middle 
of January to the middle 
of September, and also while it was falling to three inches above 
(i, i.e, until about the beginning of December. At this level 
ig Pa : : - an i’ 
2 me OO ot 
~ 
the growing points would be nipped. It is evident, therefore, 
that the three inches were grown in 10 to 104 months, which 
would make about 84 inches per annum. 
