All the country within the existing range of thermal action, and, in fact, considerably beyond it, bears the distinctive traces of the combined work of fire and water, while the ground for miles around is covered with silicious and sulphurous deposits, together with pumice, scoria, obsidian, alum, oxide of iron, and various other products, the result of the igneous and aqueous action which is everywhere observable in the form of geysers, hot springs, boiling mud-holes, _solfataras_, and _fumaroles_, and which are known to the natives under the more general terms of _ngawha, puia_, and _waiariki_.[18] All the geysers and most of the springs are intermittent, while not a few are very erratic in their movements, subsiding in one place and breaking out in another with wonderful rapidity. The water of some of the springs is as blue and as bright as crystal, in others it is of a greenish tint, while in not a few it assumes a dirty yellow colour. Nearly every spring possesses properties peculiar to itself, and mostly all are more or less efficacious in the treatment of rheumatic and nervous complaints, and cutaneous and spinal disorders. [Illustration: NATIVE VILLAGE. (_Lake Rotoiti_). _Page 62._] Upon analysis, the springs are found to contain various chemical ingredients, but in different proportions, according to the quality or properties of the water. Among the principal chemical bodies may be mentioned the chlorides of sodium, potassium, lithium, calcium, and magnesium; the sulphates of soda, lime, potash, magnesia, alumina, and iron; the silicates of soda, lime, and magnesia. In the acids, hydrochloric, sulphuric, and muriatic are found in abundance, while both sulphuretted hydrogen and carbonic acid gas are largely evolved.