vironment from the vasty deep of the past.

_The Famous Como Bluffs._ The circumstances leading up to our
discovery serve to introduce the story. From 1890 to 1897 we had been
steadily delving into the history of the Age of Mammals, in deposits
dating from two hundred thousand to three million years back, as we
rudely estimate geological time. In the course of seven years such
substantial progress had been made that I decided to push into the
history of the Age of Reptiles also, and, following the pioneers,
Marsh and Cope, to begin exploration in the period which at once marks
the dawn of mammalian life and the climax of the evolution of the
great amphibious dinosaurs.

In the spring of 1897 we accordingly began exploration in the heart of
the Laramie Plains, on the Como Bluffs. On arrival, we found numbers
of massive bones strewn along the base of these bluffs, tumbled from
their stratum above, too weather-worn to attract collectors, and
serving only to remind one of the time when these animals--the
greatest, by far, that nature has ever produced on land--were monarchs
of the world.

Aroused from sleep on a clear evening in camp by the heavy rumble of
a passing Union Pacific freight-train[21], I shall never forget my
meditations on the contrast between the imaginary picture of the great
Age of Dinosaurs, fertile in cycads and in a wonderful variety of
reptiles, and the present age of steam, of heavy locomotives toiling
through the semi-arid and partly desert Laramie Plains.

So many animals had already been removed from these bluffs that we
were not very sanguine of finding more; but after a fortnight our
prospecting was rewarded by finding parts of skeletons of the
long-limbed dinosaur _Diplodocus_ and of the heavy-limbed dinosaur
_Brontosaurus_. The whole summer was occupied in taking these animals
out for shipment to the East, the so-called "plaster method" of
removal being applied with the greatest success. Briefly, this is a
surgical device applied on a large scale for the "setting" of the
much-fractured bones of a fossilized skeleton. It consists in setting
great blocks of the skeleton, stone and all, in a firm capsule of
plaster subsequently reinforced by great splints of wood, firmly drawn
together with wet rawhide. The object is to keep all the fragments and
splinters of bone together until it can reach the skilful hands of the
museum preparator.

_The Rock Waves Connecting the Bluffs and the Quarry._ Th