So far we have only attempted to state very briefly the different kinds of rocks, and to point out that they were formed in various ways. We must now consider the question of rock-making more closely, and see what we can learn about the wonderful ways in which rocks are made; and it may be instructive to glance at the conflicting opinions on this subject which learned men held not very long ago. At the end of the last century a great controversy took place on the question of the origin of rocks, and the learned men of the day were divided into two parties. One of these parties, following the teaching of Werner, professor of mining at Freyburg, who inspired great enthusiasm among his disciples, declared that all rocks were formed by the agency of water. This was a very sweeping and of course rash conclusion. But whenever they examined rocks, they found so many clear evidences of the action of water that a powerful impression of the importance of this agency was naturally made on their minds. They found rocks uniformly arranged in great layers which extended for long distances, and containing the remains of animals which must undoubtedly have lived in the seas or estuaries. These layers were further divided into smaller layers, such as clearly were formed by the slow settling down of sand and mud. Others again contained gravels and rounded pebbles, testifying in no uncertain way to the action of water. Even the little grains of sand are obviously water-worn. This teaching was quite sound so long as they confined their attention to clays, sandstones, and limestones; but when they came to basalt and granite, a blind adherence to the views of their master caused them to shut their eyes to the clear evidences of the action of heat, presented by such rocks. The crystalline structure of such rocks; their irregular arrangement, often so different from the uniform disposition of the stratified rocks (although it must be admitted that ancient lava-flows often lie very evenly between aqueous rocks), and the way in which they burst through overlying rocks, thus proving their former molten condition; the signs of alteration exhibited in the aqueous rocks into which they intruded themselves (changes which are obviously due to the action of heat),--these and other evidences were entirely overlooked, and Werner declared that basalt had been found as a sediment under water. This school of geologists, believing so strongly in the all-powerful influence of Father Neptune, received the not inappropriate title of "Neptunists."