ction, and became convinced that at one time a great ice cap had
covered the globe down to the higher latitudes of the northern
hemisphere. So came the conception of a universal Ice Age, now one of
the accepted tenets of geology.

The dean of American geologists was Benjamin Silliman, who, at the very
beginning of the nineteenth century, took up at Yale University the work
which he was to carry on so successfully for more than fifty years. As
an inspiring teacher he was scarcely less successful than Agassiz at a
later day. His popular lectures began in 1808 and soon attracted to New
Haven the brightest young men in the country. Among them was James
Dwight Dana, who was to carry on most worthily the work which Prof.
Silliman had begun.

James Dwight Dana was attracted to Yale by Prof. Silliman's great
reputation and received there the inspiration which started him upon a
scientific career. Three years after his graduation, he was appointed
assistant to his former instructor, and two years later sailed for the
South Seas as mineralogist and geologist of the United States exploring
expedition commanded by Charles Wilkes. He was absent for three years
and spent thirteen more in studying and classifying the material he had
collected. He then resumed his work at Yale, succeeding Prof. Silliman
in the chair of geology and mineralogy. His work was recognized
throughout the world as most important, and many honors were conferred
upon him.

Another famous name in American geology is that of John Strong Newberry.
His name is connected principally with the explorations of the Columbia
and Colorado rivers. He was afterwards appointed professor of geology
and paleontology at the Columbia College School of Mines, and took
charge of that department in the autumn of 1866. During his connection
with the institution, he created a museum of over one hundred thousand
specimens, principally collected by himself, containing the best
representation of the mineral resources of the United States to be found
anywhere.

Among the pupils of Prof. Silliman who afterwards won a wide reputation
was Josiah Dwight Whitney. Graduating from Yale in 1839, he spent five
years studying in Europe, and then, returning to America, was connected
with the survey of the Lake Superior region, of Iowa, of the upper
Missouri, and of California, issuing a number of books giving the
results of these investigations, and in 1865, being called to the chair
of geology