Page:The Journal of geology (IA journalofgeology21894univers).pdf/356

reports of the Arkansas Survey, this volume does not confine the discussion of the subject to Arkansas alone, but treats it also as a general proposition, thereby adding greatly to the usefulness of the report.

The general synopsis of the volume, given above, defines its scope. The marbles and other limestones of Arkansas are very properly discussed more in detail than any others, but a general description of these materials in other parts of the United States, as well as in the more important foreign localities, is also given. The author has not only given his own experience and investigations in the subject in Arkansas and other regions, but has collected in a systematic manner a large amount of useful information published elsewhere. He discusses also very fully the geology and chemistry of marble and limestones in general, as well as their various uses for ornamental and structural purposes, for making cement, burnt lime, etc. The discussion of the best methods of working and utilizing marbles and limestones, together with the plates illustrating these processes, will be of much use to the people of Arkansas, as well as elsewhere, in developing industries of this kind. The volume is really to be considered a text-book on marbles and other limestones, and not a report on the occurrence of these materials in Arkansas alone, though the treatment of the subject as related to that state is of course given prominence.

One of the most remarkable points brought out in the volume is the immense amount of marble contained in the state. In a belt of country lying north of the Boston Mountains and extending from near the Black River on the east to beyond Eureka Springs on the west, a distance of more than 125 miles, the marble is continuous, and the length of its winding outcrops as mapped is 2,812 miles. The combined area of the six maps necessary to represent this marble region is 4,450 square miles. This area extends east and west along the north slope of the Boston Mountains, on both sides of the White River and its tributaries, which run southeasterly in a general direction parallel with the mountains. The rocks are approximately horizontal, or dip gently to the south, and the marbles, which occur in both Silurian and Lower Carboniferous horizons, are exposed where they have been cut through by the creeks and rivers. The marbles vary greatly in quality and color, but many of them have been proved by practical tests made under the direction of the Geological Survey, to be of great strength and excellent quality. In color they vary from white to gray, pink, red, brown, and black, the gray, pink, red, and brown colors being the most com-