the theory widespread at the turn of the 19th century that rocks (including igneous rocks) originated from precipitation from water. The theory appeared during the development of geology into a science, when it was still influenced by religion and the idea of the Flood. The best-known advocates of neptunism were A. G. Werner in Germany, J. A. Deluc in France, and R. Kirwan in Great Britain.

The neptunists developed the idea that rocks had originated from the waters of a primitive (primeval) world ocean which covered the entire earth and from the waters of the Flood. On the basis of this, they extended the local order of rock stratification to all the continents. Rocks were divided into two groups: the primitive rocks, that is, those that formed by chemical crystallization from the waters of a primitive universal ocean (granite, gneisses, schists, and other igneous and metamorphic rocks), and the floetz, or stratified, rocks, which were deposited over the primitive rocks (coal, gypsum, rock salt, limestone with fossils, and other rocks). Most neptunists viewed the floetz rocks as “mechanical” deposits of the biblical Flood. After new findings increasingly contradicted this traditional scheme, Werner added the transition group of rocks and to this class assigned gray-wacke, shales, and other rocks.

According to neptunism, the entire relief of the earth’s surface formed with the floetz rocks and has been preserved unchanged to the present. Neptunism did not recognize tectonic movements, which in reality change the relief. Neptunism viewed contemporary geological agents, such as atmospheric precipitation and flowing water, as “weak” forces leading to the formation of alluvial, or residual, deposits (sand, pebbles, gravel). In the neptunist scheme, volcanic rocks were found in only a small part of the earth’s crust and formed as a result of underground coal fires. Disputes about the origin of basalt, which Werner wrongly classified in the floetz group, gave rise to the controversy between neptunists and plutonists concerning the origin of all rocks. In the 1820’s, when the volcanic origin of basalt was proved and scientific theories about igneous and sedimentary rocks were developed, neptunism began to lose its significance.