but none of the modern types of flowering plants. About at the close of the paleozoic era the Appalachian mountains were formed by the crumpling of the earth's crust in this region.
That episode of crustal crumpling is taken as the milestone to mark the end of the paleozoic and the beginning of the mesozoic era, which began at least 25,000,000 years ago. Since that time, Tennessee and neighboring states have, with minor exceptions, remained continually above sea level, so that we have to transfer our search to other localities to find the continuation of the fossil record. The mesozoic era, the fourth great era of earth's history, is frequently referred to as the age of reptiles. In practically all the stratified rocks of this era there are petrified bones and footprints which tell that cold-blooded, scaley animals with backbones and four limbs lived in great numbers on land, in the sea, and in the air. The largest and most ferocious animals that ever inhabited the lands left their bones among the fossils of that era. Animals with enough feathers to enable them to fly, yet with claws on their forelimbs and teeth in their jaws, lived then and indicate the transition forms between reptiles and birds. In the same rocks with those reptiles, most of which have long since vanished from the face of the earth, a very few fragments of quite primitive mammals have been found.
These are small and insignificant creatures, most of whom laid eggs as do a couple species of small mammals today, but who suckled their young, were warm-blooded and presumably had no scales as surface covering. For the most part the reptiles were small-brained and large-bodied; they placed their trust in strength of talon and claw, rather than in mentality and agility. Observing the earth at that time, one could not help but feel that no good could possibly come from that welter of blood-thirstiness and cruelty. Yet the small minority of puny mammals, present then, was so endowed with instinct, such as parental love for offspring, that at the end of Mesozoic time it became the dominant form of life on land, while the few reptiles which did not become extinct were for the most part banished to the swamps and deserts or other out-of-the-way places. The close of Mesozoic time, the age of reptiles, was marked by the upheaval of the Rocky mountains. In a small fraction of the lime that has elapsed since then, the entire Grand Canyon of the Colorado river has been carved by the ceaseless wear of running water. For this, and many other reasons, geologists believe that each of these eras of time should be measured in terms of tens of millions of years.
The Cenozoic era, which began 5,000,000 or 10,000,000 years ago, began as the Rocky mountains were formed. Most of the rocks of that era are still unconsolidated layers of silt or sand or volcanic ash, although some are firmly cemented into sandstone, limestone, etc. In the earliest beds deposited around the flanks of the new-born mountains of the western states, the bones of a great variety of mammals have been found. They are evidently the improved offspring of the puny mammals which had lived in constant fear of the ponderous reptiles during the preceding era. Not until about this time had there been any large quantity of the kinds or vegetation upon which modern mammals feed, and this presumably explains in part the slowness of the mammalian minority in throwing off the yoke of the reptilian majority during the age of reptiles. The first flowering plants had left their leaves and seed pods in the rocks formed during the middle of the Mesozoic era, but grasses and herbs, fruit-and-nut-bearing trees were not numerous until the beginning of the Cenozoic era.
With an abundance of the right kind of plant food and freed from reptile dominion, the mammals increased rapidly in numbers, and their bones in great variety may today be seen in the rocks of the Rocky mountains and other regions. Among those of the earliest Cenozoic strata
