34 J. LeConte— Rate of Growth of Corals. 
stones and arrowheads of a later age mingled with = bones. 
In examining the relics found in western swamps, it is always 
necessary to ‘guard against the possibility of error colrwiseas 
by the action of fires of this character. 
No. 6, 16th street, Chicago. 
a ms — Rate cs pied of Corals. From a letter to Pro- 
r J. A, by Cian JOSEPH LeConte, dated 
bares of ‘Galfer May I, 
I OBSERVE in your work on Corals and Coral Reefs, while 
discussing the rate of coral growth, you mention an interesting 
observation of Weinland on the corals about Hayti, bearing on 
this subject. This recalls to my mind a very similar observa- 
tion on a much larger scale, made b myself during the winter 
of 1851, while assisting Professor Agassiz in his examination 
of the Florida reefs. Knowing your interest in the subject, I 
send you an account of it 
Professor Agassiz and his party were at Fort Jefferson, Tor- 
ugas. Dr. Wm. L. Jones and myself had gone to examine a 
little island about 8 or 10 miles to the northwest. On return- 
ing to Fort Jefferson in a small boat, when about half way 
between the two islands and in the still shoal water on the in- 
rs of the line of reefs, to our great surprise the boat suddenly 
rounded on the close-set prongs of an extensive grove of 
bet meee ee (Madrepora cervicornis?). On examining closely 
the trees of this grove, we found: 1, That the prongs were far 
more thickly set than is usual in this species; 2. that all the 
prongs not tg of the same tree, but of all the trees of the 
whole grove, grow up to _— the same level, which at the 
time examined was very near the surface; 3. that all the 
prongs at that level were ere for a distance of one to three 
inches from the point. The lower limit of death seemed to be 
a perfectly horizontal plane. The dead points rose above it to 
various distances not exceeding three inches. We rowed 
around the margin of this grove fora dicate distance and 
found everywhere the same phenomena. I satisfied mysel 
that the whole grove, for hundreds of acres in extent, had been 
clipped in a similar manner. 
subsequent inquiry at Key West, I learned that the mean 
level of the ocean, owing pie ly to the prevalence of certain 
water the living per of the madrepores grow cca aint 
e descending water level exposes and kills them down to a 
