There are not exceeding an average of sixty-five cloudy days per year in Colorado, while there are scarcely twenty days that the sun is all the day invisible at any given point. Summer weather usually continues till October, and the autumn till January. Usually the winters are mild, followed by an early spring. In summer the temperature rarely reaches 90° and is normal at 70°. Colorado climate is beneficial not to consumptives alone, but persons of kidney and liver and kindred diseases are benefited both by climate and the mineral waters which everywhere abound in the State, and are especially numerous and available on the Denver & Rio Grande Railroad lines. The supply of coal in Colorado is inexhaustible, the lignite or brown coal area extending from St. Vrains on the north to the Raton Mountains on the south, about 220 miles in length and varying from twenty to twenty-five miles in breadth, along the eastern base of the mountains. Large portions of this field have been swept away by floods resulting from melting glaciers. The principal developments of this vast field have been made in the vicinity of Trinidad and Walsenburg, Cañon City, Coal Creek, Colorado Springs, Golden, Loveland, Erie, and Boulder. Lignite also exists in North Park and at various points on the divide between North and Middle parks. Jet, or the black variety of coal, occurs in seams from one-half to six inches in width in the shale about Cañon City and Little Fountain Creek. The most important mines of bituminous coal are the Trinidad group and the mines at Crested Butte. Anthracite coal appears to be confined mainly to the coal basins in the Elk Mountain. Native coke is found near Crested Butte, where a dyke of lava has intruded the coal strata. Official geological surveys give a coal-bearing strata of 40,000 square miles, or one-third of the entire area of the State. In 1873, when coal-mining began to take shape as an industry, the output was 69,977 tons; to-day the output is 2,373,954 tons, which comparison gives the reader some idea of the rapidity of its growth.