Ralph Stone tackled the Mystic River, and marked ledges and set stakes opposite the flood plain meanders. The idea was that ledges split by winter freezes, and that the meanders of a stream build on one side and cut on the other. Maps were made repeatedly, and the ledge cracks were measured in millimeters. Some movement was found, but a college year was not enough time. If we could combine as a motion picture, photographs from the air taken once a year for many years, doubtless the film would show that the stream meander pattern is migrating toward the sea like a wiggling snake.
Stone next made a model three inches thick in a tank of water, by sedimenting sixty-one very thin layers of marble dust, coal dust, clay, red lead, and sand. He tipped it up as an island and sprayed it in periods which lasted one to ninety-two hours, up to a total of 719 hours. A forking stream and its delta were formed in the lagoon of the tank. The stream cut a canyon with waterfalls, treelike branches, esplanades, and a flood plain. There were three principal hard white multiple strata layers in the model, separated by sand. The white layers made waterfalls and were eaten back to form the canyons.
When the cross section of the delta was sliced with a knife, it showed three white layers foreset at thirty degrees under the tank pool and separated by more sandy strata. The bottommost of these was the sediment of the top thick marble dust layer of the model as first eroded by the spray, and the top frontal layer of the leaf-shaped delta was the product of the erosion of the canyon bottom on the lowest of the white layers. This must happen in nature where one formation in reverse order is derived by river erosion undermining a stratified older pile of sediments.
We called this the Grand Canyon model, and it showed many features similar to those of South Dakota Bad Lands and the Colorado River drainage. It was strictly rainfall erosion and stratification soakage and seepage. The model surface sloped ten degrees, the high divide at the top had a backslope of forty-five degrees, and everything was sprayed for two months with special hose nozzles, making during part of each day a mistlike rainfall.
The steep backslope did not trench itself at all despite its steepness. This slope, on the contrary, absorbed moisture and carried the rainfall underground down the dip of the strata to add spring water to the main streams. The backslope was a “steep escarpment,” supposed in physical geography to migrate by trenching backward, but the rills never gained volume enough to cut into it. All the water volume acquired its grit for cutting from the large surfaces, which were gradually tilted in the direction of the rivers.
When the complete series of experiments on erosion and sediment was published, it showed that the treelike branching of rivers is dependent on underground water surfaces; that meanders on a flood plain are partly a bubbling-up process of flood-plain soakage; that when side tributaries form by undermining, the upstream branches cut off underground water from the downstream branches; and that when a country is tilted in one direction, there is a tendency to parallel streams, separated by intervals controlled by underground water areas reached by the undermining tracery of headwater springs.
This arborescence in a spray model is a regular and delicate adjustment, where a bunch of tributaries is not mere catchment of rainfall, but is the product of sheet flood in belts of underground water related to the tilt of the country. Arborescence of river drainage on a surface of flat strata, like the coastal plain of the southeastern United States, is a rhythmical pattern of exquisite design capable of reproduction and study in the laboratory. It is a mathematical forking and headward development dependent on volume of water, undermining impermeable strata along permeable ones. And after the “tree” map is formed, the bulb of branches and twigs and underground leaves of spring water holds all the downslope country in its “shadow,” so that no new rivers can form there. This is what makes our great maps of river systems. It is not haphazard. It is a vast ocean of underground water, with mountains of water and valleys of water.
A great lake marks an underground soakage water level. A riverbed marks an underground seepage topography. The sea of water inside a continent is just as much a map of hills and dales of water as the land is a map of the hills and valleys of geography. The water is dynamic, it is flowing. The land surface is dynamic and rain fed; it is creeping soils. Together, groundwater and rivers are melting down the landscape as a living thing. Man dams the water and uses the power of the erosion melting down the land.
When we went to Haystack Basin north of the Yellowstone Park, we found that all of the mountains surrounding it were audibly crumbling. Ultimately, the continent is all one thing: a falling body of rotten rock, ice, water, sand, boulders, and soils, self carved into valleys and mountains, always tumbling. And down below are the fault blocks, prisms of earth shell over the white hot core. And that also is eternally in motion, irrupting, earthquaking, lifting, falling, scraping, heating, cooling in waves through the ages. Man is very tiny, but if he listens he can hear the earth’s heartbeats.
At hot springs the water mantle meets the hot earth shell. So the geyser basins of Yellowstone, California, New Zealand, and Iceland are a hot part of the great erosion system of groundwater. This brings us to the next group of experiments, the making of artificial geysers.