and expanded-these dimensions far excelling any foreign spruce.

Five of our firs, the Red-bark, the White-bark, and the Shasta firs of California, and the Grand and Noble firs of the region northward, become two or three times as large as any eastern or foreign fir, being often 200-300 feet high, 12-18 feet in diameter, with cones 6-8 inches long.

Our two world-renowned redwoods-the Coast Redwood and the Sierra Big Tree, rising to the height of 300-320 feet and enlarging, while yet young, to a diameter of 20-35 feet and growing for 3,000-5,000 years-are not approached in grand proportions and regal majesty elsewhere. And the cones of one of our redwoods-the Sierra Big Tree-though small as compared with our pine cones, are yet, doubtless, the monsters of their race, the largest being the size of a hen's egg, while the largest cone found in connection with fossil remains of the twenty-five extinct species do not exceed the size of a nutmeg.

So with the 2-3 inch cones of our Alpine Hemlock Spruce, the 1-inch cone of Incense Cedar, the 11⁄2-inch cone of the Monterey Cypress, the %inch berry of the California Juniper, and the California False Nutmeg, all the largest cones of their respective families.

WHY THIS FAVORITISM?

This prodigality in number and size extends to other vegetable growths. Our oaks are numerous and often large, with the largest acorns and cups known. One of our maples bears leaves 6-10

inches across, while the little popgun elder of the East is supplanted here by a species 12-20 inches in diameter.

Most of the trees mentioned are indigenous to California and three-fourths of them are found only in that state. Why this great prodigality of Nature in behalf of the Pacific Slope, and especially of little California?

The solution of this problem involves a brief discussion of certain controlling factors.

At the outset we may observe that an impassable climatic barrier is set up at present, by Nature, preventing migration north and south. The Torrid Zone, in which no resinous trees can grow except on high peaks, separates the world's forests into unequal and very different floras.

The Southern Hemisphere is the home of the Araucaria, the Eucalyptus and the Acacia, while in the Northern Hemisphere are found-in addition to the hosts of broad-leaved, non-resinous trees, such as oak, ash, hickory, etc.—all of the large families of pine, larch, cedar, spruce, and fir, with the redwood, cypress, and juniper; the distribution of these trees across the two continents, however, is very unequal.

DISPARITY OF AREAS AND DISTRIBUTION.

across.

The northern part of the eastern continentEurasia—is approximately 9,000 miles North America is but 3,000. We would naturally expect, for instance, three times as many pines in Eurasia as in America. Just the reverse is the case. Of the 80 species of known pines only 20

are indigenous to Eurasia while 60 are flourishing in America.

Again, the Pacific Slope region, from the Rocky Mountains to the Pacific shore, is about 1,000 miles, one-third of the distance across, yet it has 40 out of the 60 American species, 15 being in Mexico and 25 in the western United States, with 20 of these in California, a narrow strip of coast only 800 miles long by 150 wide, yet containing as many pines as all Eurasia!

Now if the distribution was equal, Eurasia having 60 pines and North America 20, the Pacific Slope, being one-third of America, would be entitled to but 6 species, and little California, which embraces about one-tenth of the Pacific Slope, would have little more than half a chance to get one species!

This excessive prodigality of Nature in favor of the Pacific Slope and especially the California part of it, is due to a combination of factors, chief of which are the contours of continents, the trend of principal mountain ranges, the behavior of certain oceanic and atmospheric currents, the alternate elevation and depression of continental areas, together with the ability of all these factors to modify the effects of certain crucial climatic periods, called—

THE ICE AGE AND THE THERMAL AGE.

The phenomenon of hot and cold periods in the earth's history compelling the migration, the change of location of the entire organic worldthe kingdoms of the animals and plants-is a

much discussed and controverted topic. Seven theories have been presented from time to time, accounting for these important epochs, chief of which is the very interesting—

ASTRONOMICAL THEORY.

This theory, first presented by Mr. Croll, and endorsed by Professor Geikie and many other English geologists, "attributes the Glacial Age to the combined influence of precession of equinoxes and secular changes in the eccentricity of the earth's orbit," whereby the seasons, summer and winter. would have a disparity of nearly five weeks instead of one week, as at present: this disparity, it is claimed, would produce Glacial and Thermal Ages alternately, every 21,000 years.

However, Professor Le Conte, America's most renowned geologist, controverts this theory, in part, quoting from many authorities, showing that but one Glacial Age can be proven. Referring to the researches of Professor Wallace and others he asserts that the phenomenon is the result of several agencies-astronomical, geological, and geographical-producing a severe Glacial Age of great length, with two cumulative periods of greatest severity and a Sub-Thermal period between; the Age commencing about 240,000 years ago, continuing 160,000 years, and ending 80,000 years ago.

GREAT DESTRUCTION BY COLD.

During this Glacial Age the plants were driven slowly, generation after generation, a few feet at a time, down across the North Temperate Zone, by

a world-wide sheet of ice, to be as slowly driven back by waves of tropic heat.

In this double migration, owing to the configuration of continents and mountain ranges, most of the plants were destroyed, only a few vestiges of the post-glacial families being extant, to-day, gathered here and there upon the plains or stranded upon the mountains.

The means and manner of this destruction are most interesting. The continents of both the old and new world are greatly expanded at the north, while the southern portions are attenuated to narrow peninsulas.

These configurations give to the North Temperate Zone its greatly dominant character, having most of the existing families, while the peninsulas are sparsely furnished.

The Eurasian mountain ranges are mostly transverse, like the Alps, Himalayas, and Thian-Chan Mountains, forming barriers to the progress of plants; while North-American ranges are nearly longitudinal, permitting the plants to escape southward during a Glacial Age, and return during a Thermal one.

There is much evidence found as fossils in the rock strata, that an abundant flora of monster trees once occupied the Arctic regions, similar on the two continents, owing to connections then existing or to nearness of extremities.

MANNER OF THIS DESTRUCTION.

The formation of an ice-cap at the pole and of snow and ice deposits on the summits of mountains lower down in latitude, drove the plants down