The stream is believed to find its outlet at a spring about three miles from the entrance to the caves. This spring is of great size and volume, and flows with remarkable swiftness. In rainy seasons the spring boils and gushes as if choked with the flood of water that pours from its mouth. The stream in Black Prairie cave rises when there is a heavy rainfall in the surrounding country, and the increased flow of both springs and stream at such times is taken as evidence that they are connected.
ARTESIAN WATERS IN TEXAS.
In the south central part of Texas is an upland covering an area of 14,000 square miles, and known as the Edwards Plateau. At the southeastern foot of this elevated tract there is no end of gushing springs, which form the headwaters of the San Antonio and San Marcos rivers. In a big State like Texas, the rainfall of one locality often varies a good deal from that of adjacent regions. But, according to a bulletin of the United States Geological Survey, the fluctuations of discharge of the streams just mentioned correspond closely to the rainfall up on the plateau, from which it is inferred that some invisible connection exists between the springs and the upland. The bulletin declares that this similarity has been found to hold true for dry and wet years alike. The Edwards Plateau is a flat, grass covered upland. The rain which falls upon it does not flow off in surface streams, but sinks into the porous soil, and eventually finds its way underground to the bold scarp line of the region, where it bursts out in abundant springs.
The San Antonio River has its source in one of these artesian springs, and between it and the wells driven to supply water to the city of San Antonio there seems to be close connection, shown in their mutual changes, which indicates that their waters have a common source. It was recently noticed that when the wells were steadily drawn upon for twenty-four hours the water level of the head lake of the river fell several inches, but that on shutting off the wells the lake regained its level in about one day. So intimate is the relation between the flow of the wells and that of the river that it is always possible to tell how high the water will rise in the former by observing the river’s height on a gauge rod placed upon its bank.
THE GREAT ASSAM EARTHQUAKE.
A thorough report of the earthquake in Assam, in 1897, the most violent and extended earthquake of historic times, has been made by Mr. R. D. Oldham. From an abstract by Prof. Davis of Harvard University, it appears that an area of 150,000 square miles was laid in ruins, all means of communication interrupted, the hills rent asunder and cast down in the landslips, the plains fissured and riddled with vents from which sand and water poured forth in astounding quantities, causing floods in the rivers, etc. A surrounding area of 1,750,000 square miles felt a shock of unusual energy. The earthquake wave traveled at the rate of 120 miles a minute. The vertical displacement of the ground near the center of disturbance was probably as much as fourteen inches—an unprecedented quantity; the vertical movement of earthquakes of great violence, like the Charleston earthquake, is seldom more than two inches.
Some of the results of this great earthquake of June 12, 1897, are astonishing. Faults were produced, one having a throw of 25 feet and a length of 12 miles; another a throw of 10 feet and a length of 2½ miles. The larger of the two dammed a river so as to form a lake several miles in extent and ruining a forest of at least 50,000 trees. Landslides of great magnitude were produced in the Himalayas and the valleys of streams were changed beyond recognition.