Unprecedented population increases have occurred since World War II. mostly in those countries with low agricultural productivity and low per capita incomes. Population growth coupled with rising energy costs and worldwide inflation has taxed the ability of farmers to meet human food requirements. In fact, in some areas. such as sub-Saharan Africa. the per capita food production has actually declined in the past decade.

This volume reproduces some of my published articles on the history of the natural sciences. I have used three criteria in making the selection. First, all these articles focus on the late eighteenth and early nineteenth centuries – or on what political historians often call “the age of revolution” – although a few range over a longer timespan. Second, all of them deal with the area of natural knowledge that at just this time was being transformed into the science of “geology”.

The Getchell veins are lenticular replacement bodies lying along arcuate branches of a complex range-front fault system. The fault zone cuts all rocks of the district and is tentatively dated as late Tertiary.

The more intensely mineralized portions of the deposit form a shallow blanket with roots that project downward into areas of sparse mineralization.    The gold shoots are restricted to areas of intense mineralization.

Native gold and native silver are the only economic minerals. The great bulk of the gold occurs in minute but microscopically visible particles. Some gold may also occur in submicroscopic particles and some may be in solid solution in pyrite and carbon.

The ore minerals, dissolved in alkali sulfide solutions, are believed to have been deposited when the sulfide ion concentration in the hydrothermal liquid decreased, making unstable the double sulfides of gold-, iron, and arsenic.

The Getchell deposit is similar in many ways to the Nevada quicksilver deposits and present-day hot-spring deposits. The Getchell ore occurrence may represent a gradation from the common epithermal gold deposit to the cinnabar deposit. It is therefore placed close to the feeblest end of the epithermal group.

The study of rocks and other mineral associations, especially of ore deposits, starts out from the purely descriptive. The composition of these materials, their geologic position in the most comprehensive sense, and their gross and fine structures and textures, etc., must be established. Further research must explain, first the "How"', then the "Why". The latter must comprise the interpretation of the association of materials and geologic position as well as each detail of texture and structure, even the smallest. On the knowledge obtained, one must build further and must generalize. Things of which the "Why" can be explained directly will serve in the explanation of others. In doing this the danger of circular reasoning will exist ; criticism is therefore invariably necessary, self-criticism most of all. The interpretations must, if possible, be reached along several paths, and the validity of the various paths must be carefully considered. <...>