164 TRANSACTIONS OF THE [APR. 22, 
less a piece broken apparently from the lip of a large conch, and 
of uncertain use, could be so regarded. This mound was found 
to be very extensive ; and he would estimate the time required 
for its construction as perhaps four hundred years,—supposing 
the population of the islet to have amounted to two thousand. 
Some of the shells of which it is composed are still abundant on 
the coast, while others are now rarer, and one species at least has 
undoubtedly become extinct. 
Dr. NEWBERRY said that he also had examined this mound, 
when on a visit to Florida some years previous. He observed a 
large live-oak tree growing upon it, indicating of course that a 
long period had elapsed since the mound had been abandoned 
and ceased to receive additions. Dr. Friedrich’s computation of 
four hundred years, for the time taken to form the mound, 
was a minimum period. It was probably much longer, as the 
population of the islet could scarcely have been at any time so 
large as two thousand. He had succeeded in finding a human 
skull in the mound, and part of a skeleton. 
Mr. Joun C. HENDERSON read the paper announced for the 
evening, entitled 
THE TEHUANTEPEC SHIP RAILWAY. 
Conterminous for fourteen hundred or more miles with the 
southern border of the United States, lies the Republic of Mexico, 
—a country with an area about sixteen times that of the great 
State of New York. 
South of Mexico for about twelve hundred miles, extends a 
beautiful and fertile region, whose width varies from about three 
hundred to about twenty-eight miles. This picturesque land 
may be viewed as a great causeway, uniting North and South 
America, and dividing, in the middle of the American conti- 
nent, the waters of the Atlantic Ocean from the Pacific main. 
Its superb scenery is diversified by a chain of mountains extend- 
ing almost its entire length and having peaks which rise from 
three thousand to fourteen thousand feet above the waters of 
the oceans. From a geographical point of view, the great isth- 
mus which unites the two Americas should be considered as 
embracing a part of Mexico and as being about fourteen or fifteen 
hundred milesinlength. Itsarea is about three hundred thousand 
square miles,—an area out of which six States of the size of New 
York could be formed. This isthmus is a vast natural bridge,— 
