Left on this trail to FERTILE VALLEY LAKE NO. 2, =1 m.=, largest of the several shallow lakes in this vicinity which contain millions of tons of sodium sulphate, a valuable mineral resource. These lakes and sloughs, with no drainage outlets, are part of a linear series lying NW. to SE. along a preglacial stream course. The beds range from a few inches to as much as 80 ft. in depth. Because of the low rainfall in recent years many of the lakes glisten white in the sunlight. Literally, a wild goose chase led to the discovery of these sodium sulphate deposits. A Grenora hunter waded into a shallow lake to recover a goose which had fallen into the water, and found the lake bottom covered with a hard crystal formation resembling salt deposits he had seen in Canada, which he knew to be commercially valuable. He directed attention to the lake, and as a result an FERA survey was undertaken in 1934, and a large amount of the mineral was found here. Fertile Valley Lake No. 2 was estimated to contain 11,000,000 tons, and two other lakes in the vicinity 5,000,000 and 1,750,000 tons each. Sodium sulphate is also known as Glauber's salt. Commercially it has a value of about $20 a ton, and is used medicinally, in paper manufacture, as salt for cattle, and in manufacturing soap and munitions. In 1937 the University of North Dakota, in cooperation with the State Highway Department, was conducting experiments to determine the value of sodium sulphate in highway construction. At present there is little demand for North Dakota sodium sulphate because of the accessibility of sources nearer the points of consumption. At =21 m.= is the junction with another county dirt road; =R.= on this road to the junction with a county highway, the Grenora-Alkabo route, at =23 m.=; =R.= on this road; at 30 the route turns =L.= and proceeds up a hill to WRITING ROCK STATE PARK, =30.3 m.= Of gray granite, Writing Rock stands in a slight hollow on the crest of a hill, commanding a wide view of the surrounding country. The top and two sides of the rock are covered with hieroglyphs, consisting of lines, dots, circles containing dots, and, near the top, a flying bird. Many attempts have been made to decipher the writing, which apparently was carved into the rock at several different periods. Whatever the meaning of the inscriptions, the rock is regarded as sacred by Indians who, even after the settlement of the State, made pilgrimages here from the Fort Peck (Mont.) Reservation and other distant points. The site, because of its elevation, served advantageously for smoke signals. Several graves have been found in the vicinity, and excavations have revealed hammers, hatchets, arrowheads, sea shells, elk teeth, and beads of many shapes and colors. One grave is said to have yielded beads that measured 52 ft. when strung.