The Age of Reptile developed a wide variety of monsters in the central regions of the continent from Montana to the Gulf of Mexico. The dinosaurs of the Triassic and Jurassic periods sometimes had gigantic size, the Brontosaurus attaining a length of sixty feet or more. The femur of the Brachiosaurus exceeded six feet; this must have been the greatest of them all.
The greater dinosaurs were herbivorous. The carnivorous species were not remarkable for size; there were small leaping forms scarcely larger than rabbits. The necessity for defense against the flesh-eaters developed, in the smaller dinosaurs, extremely heavy armor. The stegosaur carried huge plates upon his curved back, suggesting a circular saw; his long powerful tail was armed with sharp spikes, and must have been a dangerous weapon. Dinosaurs roamed all over what is now called our middle west.
In those days the central part of our land was warm and swampy. Fresh-water lagoons and sluggish streams were bordered by low forests of palms and ferns; one must go to the tropics to find a corresponding landscape in our times. The waters abounded in reptiles and fish. Huge winged reptiles flew from cover to cover. The first birds were evolving from reptilian forms.
The absorbing story of these times is written in the rocks. The life forms were at their full when the sands were laid which to-day is the wide-spread layer of sandstone which geologists call the Morrison formation. Erosion has exposed this sandstone in several parts of the western United States, and many have been the interesting glimpses it has afforded of that strange period so many millions of years ago.
In the Uintah Basin of northwestern Utah, a region of bad lands crossed by the Green River on its way to the Colorado and the Grand Canyon, the Morrison strata have been bent upward at an angle of sixty degrees or more and then cut through, exposing their entire depth. The country is extremely rough and bare. Only in occasional widely separated bottoms has irrigation made farming possible; elsewhere nothing grows upon the bald hillsides.
Here, eighteen miles east of the town of Vernal, eighty acres of the exposed Morrison strata were set aside in 1915 as the Dinosaur National Monument. These acres have already yielded a very large collection of skeletons. Since 1908 the Carnegie Museum of Pittsburgh has been gathering specimens of the greatest importance. The only complete skeleton of a dinosaur ever found was taken out in 1909. The work of quarrying and removal is done with the utmost care. The rock is chiselled away in thin layers, as no one can tell when an invaluable relic may be found. As fast as bones are detached, they are covered with plaster of Paris and so wrapped that breakage becomes impossible. Two years were required to unearth the skeleton of a brontosaurus.
The extraordinary massing of fossil remains at this point suggests that floods may have swept these animals from a large area and lodged their bodies here, where they were covered with sands. But it also is possible that this spot was merely a favorite feeding-ground. It may be that similarly rich deposits lie hidden in many places in the wide-spread Morrison sandstone which some day may be unearthed. The bones of dinosaurs have been found in the Morrison of Colorado near Boulder.
For a hundred and twenty-five or thirty miles southwest of the Grand Canyon, the valley of the Little Colorado River is known as the Painted Desert. It is a narrow plain of Carboniferous and Triassic marls, shales, sandstones, and conglomerates, abounding in fossils, the most arid part of Arizona; even the river’s lower reaches dry up for a part of each year. But it is a palette of brilliant colors; it will be difficult to name a tint or shade which is not vividly represented in this gaudy floor and in the strata of the cliffs which define its northern and eastern limits. Above and beyond these cliffs lies that other amazing desert, the Navajo country, the land of the Rainbow Bridge and the Canyon de Chelly.
I have mentioned the Painted Desert because it is shaped like a long narrow finger pointed straight at the Petrified Forests lying just beyond its touch. Here the country is also highly colored, but very differently. Maroon and tawny yellow are the prevailing tints of the marls, red and brown the colors of the sandstones. There is a rolling sandy floor crisscrossed with canyons in whose bottoms grow stunted cedars and occasional cottonwoods. Upon this floor thou-sands of petrified logs are heaped in confusion. In many places the strong suggestion is that of a log jam left stranded by subsiding floods. Nearly all the logs have broken into short lengths as cleanly cut as if sawn, the result of succeeding heat and cold.
Areas of petrified wood are common in many parts of the Navajo country and its surrounding deserts. The larger areas are marked on the Geological Survey maps, and many lesser areas are mentioned in reports. There are references to rooted stumps. The three groups in the Petrified Forest National Monument, near the town of Adamana, Arizona, were chosen for conservation because they are the largest and perhaps the finest; at the time, the gorgeously colored logs were being carried away in quantities to be cut up into table-tops.
As a matter of fact, these are not forests. Most of these trees grew upon levels seven hundred feet or more higher than where they now lie and at unknown distances; floods left them here.
The First Forest, which lies six miles south of Adamana, contains thousands of broken lengths. One unbroken log a hundred and eleven feet long bridges a canyon forty-five feet wide, a remarkable spectacle. In the Second Forest, which lies two miles and a half south of that, and the Third Forest, which is thirteen miles south of Adamana and eighteen miles southeast of Holbrook, most of the trunks appear to lie in their original positions. One which was measured by Doctor G. H. Knowlton of the Smithsonian Institution was more than seven feet in diameter and a hundred and twenty feet long. He estimates the average diameters at three or four feet, while lengths vary from sixty to a hundred feet.
The coloring of the wood is variegated and brilliant. “The state of mineralization in which most of this wood exists,” writes Professor Lester F. Ward, paleobotanist, “almost places them among the gems or precious stones. Not only are chalcedony, opals, and agates found among them, but many approach the condition of jasper and onyx.” “The chemistry of the process of petrifaction or silicification,” writes Doctor George P. Merrill, Curator of Geology in the National Museum, “is not quite clear. Silica is ordinarily looked upon as one of the most insoluble of sub-stances. It is nevertheless readily soluble in alkaline solutionsi. e., solutions containing soda or potash. It is probable that the solutions permeating these buried logs were thus alkaline, and as the logs gradually decayed their organic matter was replaced, molecule by molecule, by silica. The brilliant red and other colors are due to the small amount of iron and manganese deposited together with the silica, and superoxydized as the trunks are exposed to the air. The most brilliant colors are therefore to be found on the surface.”
The trees are of several species. All those identified by Doctor Knowlton were Araucaria, which do not now live in the northern hemisphere. Doctor E. C. Jeffrey, of Harvard, has described one genus unknown elsewhere.
To get the Petrified Forest into full prospective it is well to recall that these shales and sands were laid in water, above whose surface the land raised many times, only to sink again and accumulate new strata. The plateau now has fifty-seven hundred feet of altitude.
“When it is known,” writes Doctor Knowlton, “that since the close of Triassic times probably more than fifty thousand feet of sediments have been de-posited, it is seen that the age of the Triassic forests of Arizona can only be reckoned in millions of years just how many it would be mere speculation to at-tempt to estimate. It is certain, also, that at one time the strata containing these petrified logs were them-selves buried beneath thousands of feet of strata of later ages, which have in places been worn away sufficiently to expose the tree-bearing beds. Undoubtedly other forests as great or greater than those now exposed lie buried beneath the later formations.”
A very interesting small forest, not in the reservation, lies nine miles north of Adamana.
The popular idea of a desert of dry drifting sand unrelieved except at occasional oases by evidences of life was born of our early geographies, which pictured the Sahara as the desert type. Far different indeed is our American desert, most of which has a few inches of rainfall in the early spring and grows a peculiar flora of remarkable individuality and beauty. The creosote bush seen from the car windows shelters a few grasses which brown and die by summer, but help to color the landscape the year around. Many low flowering plants gladden the desert springtime, and in the far south and particularly in the far southwest are several varieties of cactus which attain great size. The frequenter of the desert soon correlates its flora with its other scenic elements and finds all rich and beautiful.
In southwestern Arizona and along the southern border of California this strange flora finds its fullest expression. Here one enters a new fairy-land, a region of stinging bushes and upstanding monsters lifting ungainly arms to heaven. In 1914, to conserve one of the many rich tracts of desert flora, President Wilson created the Papago Saguaro National Monument a few miles east of Phoenix, Arizona. Its two thousand and fifty acres include fine examples of innumerable desert species in fullest development.
Among these the cholla is at once one of the most fascinating and the most exasperating. It belongs to the prickly pear family, but there resemblance ceases. It is a stocky bush two or three feet high covered with balls of flattened powerful sharp-pointed needles which will penetrate even a heavy shoe. In November these fall, strewing the ground with spiny indestructible weapons. There are many varieties of chollas and all are decorative. The tree cholla grows from seven to ten feet in height, a splendid showy feature of the desert slopes, and the home, fortress, and sure defense for all the birds who can find nest-room behind its bristling breastwork.
The Cereus thurberi, the pipe-organ, or candelabrum cactus, as it is variously called, grows in thick straight columns often clumped closely together, a picturesque and beautiful creation. Groups range from a few inches to many feet in height. One clump of twenty-two stems has been reported, the largest stem of which was twenty feet high and twenty-two inches in diameter.
Another of picturesque appeal is the bisnaga or barrel cactus, of which there are many species of many sizes. Like all cacti, it absorbs water during the brief wet season and stores it for future use. A specimen the size of a flour-barrel can be made to yield a couple of gallons of sweetish but refreshing water, whereby many a life has been saved in the sandy wastes.
But the desert’s chief exhibit is the giant saguaro, the Cereus giganteus, from which the reservation got its name. This stately cactus rises in a splendid green column, accordion-plaited and decorated with starlike clusters of spines upon the edges of the plaits. The larger specimens grow as high as sixty or seventy feet and throw out at intervals powerful branches which bend sharply upward; sometimes there are as many as eight or nine of these gigantic branches.
No towering fir or spreading oak carries a more princely air. A forest of giant saguaro rising from a painted desert far above the tangle of creosote-bush, mesquite, cholla, bisnaga, and scores of other strange growths of a land of strange attractions is a spectacle to stir the blood and to remember for a lifetime.