Intelligence and Miscellaneous Articles. 319 
toned is observed to act more powerfully on the higher than vice 
versa. 
For a counterproof, the string which just now was the lower can 
be stretched more strongly, so that it becomes the higher, &c. 
The limits of the excitability moreover follow the length, thick- 
ness, and tension. TTith short, thick, strongly stretched strings 
the limit of excitability of the higher by the deeper-toned lies at a 
difference of 1 or 2 vibrations in a second. 
With tuning-forks, particularly those with short thick prongs, 
the difference of the numbers of vibrations must not amount to 1, 
if the deeper-toned is to be able to excite the higher. It was, 
however, on tuning-forks that I first observed the phenomenon. I 
had two forks upon equal resonators, which were said to have 
exactly the same pitch. I placed them over against one another, 
and struck one of them, when the other did not sound with it ; but 
when I struck the other, the first replied very audibly. Having 
found out which of the two forks gave the higher tone, I loaded 
one of its prongs with a little wax, and, by repeated alteration of the 
loading, easily arranged so that each fork was in a condition to 
excite the other with equal force. I now augmented the load of 
the originally higher-toned fork, and found that now this coidd 
excite the other, but not vice versa. — "Wiedemann's Aanalen, xix. 
pp. 935, 936. 
ELEVATED CORAL REEFS OF CUBA. 
BY W. 0. CROSBY*. 
Mr. Crosby describes in this paper the elevated coral reefs of Cuba, 
and draws from them the apparently well-sustained conclusion that 
they indicate a slow subsidence during their formation, and hence, 
further, that Darwin's theory of the origin of coral islands is the 
true theory. The lowest reef-terrace of the northern side of the 
island has a height of 30 feet, and varies in width from a few rods 
to a mile ; it was once plainly the fringing reef of the shore. The 
second reef-terrace rises abruptly from the level of the lower to a 
height of 200 to 250 feet, and bears evidence of having been of like 
origin with the lower. The altitude of the third reef is about 500 
feet ; and the fourth has a height east of Baracoa, near the Yumiui 
Eiver, " of probably not less than 800 feet." These old reef- 
terraces extend, " with slight interruptions, around the entire coast 
of Cuba ; and in the western part of the island, where the erosion 
is less rapid than further east, they are the predominant formation, 
and they are well preserved on the summits of the highest hills. 
Mr. Alexander Agassiz states that the hills about Havanna and 
Matanzas, which reach a height of over 200 feet, are entirely com- 
posed of reef-limestone." 
In the precipitous mountain called El Yunque (the Anvil), five 
miles west of Baracoa, reef-limestone, 1000 feet thick, constitutes 
the upper half of the mountain, tbe lower part, on which the reef 
rests, consisting of eruptive rocks and slates : and originallv tbe 
upper limit of this modern limestone formation must have been 
* Proc. Boston Soc. Xat. Hiit. 
