Volcanic rocks _____________________________________ _ Monchiquite province __________________________ _ Minette province ______________________________ _ Basalt province ________________________________ _ Hydrology of the volcanic rocks _____________________ _ Diatremes ____________________________________ _ Chemical quality of the ground water ____________ _ Development of ground water ___________________ _ Literature cited ___________________________________-_ ILLUSTRATIONS FRONTISPIECE. Photograph of Boundary Butte, one of the isolated volcanic necks in the Navajo country. PLATE 1. Map showing distribution of the Cenozoic igneous rocks and the location of selected wells and springs, Navajo