GEOLOGICAL PREFACE.

THE extended experience of one of the authors in the work of a mining engineer and geologist has convinced him that it is absolutely necessary to have a clear understanding of the differences between the various kinds of mineral deposits and their mode of occurrence in nature, and also to know something of their origin, in order to properly appreciate any of the legal questions which have arisen in connection with them. In fact, some important legal distinctions are founded entirely upon these physical, or more properly, geological differences.

Every lawyer who has a large practice in mining law should therefore have some knowledge of geology, and to such the author is glad to recommend the admirable works of Prof. Joseph Le Conte. By a careful study of these works he can get a better idea of American geology and of the fundamental principles of geology in general than from any other work with which the author is familiar.

The information contained in the following pages a large portion of which is very generally recognized by those versed in geological science, but which is not at all well understood by those unfamiliar with such science will be sufficient, however, it is hoped, to give a general idea of the subject, and enable the reader to have a clearer understanding of many of the physical and geological differences between the various kinds of mineral deposits, and therefore to better appreciate the reason for the legal distinctions which are based upon these differences.1

1 For the definition of the term "mineral" in a legal sense, see page lxxvi, under division "Natural Gas."

For a more complete description of the characteristics, the mode of occurrence

and uses of the minerals herein referred to, see a work by the author under the title of " A Description of Minerals of Commer cial Value." published in 1897 by John Wiley & Sons, New York.

GENERAL GEOLOGY.

All rocks known to us are of two great classes, sedimentary and eruptive.

FIRST. Sedimentary Rocks, as implied by their name, are those which are of sedimentary origin. That is to say, they originated in accumulations, through the distributing agency of water, of (1) either rounded or angular pebbles or sand (minute quartz pebbles) of (2) mud or finely divided clay, and of (3) calcareous silt (coral mud) or sometimes of minute shells, at the bottom of seas, lakes, and rivers.

These three kinds of sediments, when consolidated, have made respectively pebble beds (conglomerates or breccia) or sandstones, shale or slate beds, and limestones.

By far the great majority of these, and always the first two, must have been derived from the ruin or breaking down of other rocks, either eruptive or stratified, or both, composing land areas, and it therefore appears that most of these rocks are of littoral or near shore origin. The first two, sandstone and shale, differ from each other only in the degree of fineness to which the detached fragments have been ground in the process of erosion, which will be referred to later.

Limestones, in many cases, have also had a somewhat similar origin. They have been formed by the degradation of great coral reefs and the subsequent pulverization of the detached fragments forming coral sand, or more frequently coral mud. It is thought. by some that limestone beds have frequently been formed by the precipitation of carbonate of lime in the sea water. This theory of chemical origin may possibly be true in some cases, but the former physical theory of origin is regarded as more probable in the majority of cases. As might be inferred, many limestones have been formed from the erosion of pre-existing limestones, the fine granules being carried mechanically in suspension in water, and finally deposited as a sediment. Of course in the same way many beds of sand and of mud are derived from preexisting sandstone and slate strata. Some limestone, chalk, and marble beds, however, are formed entirely from an accumulation (and subsequent consolidation) of myriads of small calcareous sheils upon the sea bottom,deep-sea ooze, for example; yet

all limestones are apt to contain various kinds of shells as they originally existed in a matrix of coral mud, in much the same way that shells on the sea floor, from very remote geological periods to the present, have become imprisoned in an accumulating bed of sand or of mud, which was brought to its present position through the agency of rivers or of ocean currents. With the exception of the so-called Primitive and Algonkian rocks (and in these they have probably been obliterated, owing to the fierce and numerous bakings which the rocks have received) nearly all sedimentary rocks contain evidence of many of the life forms existent in the ages when, as sediments, they were laid down. Of course these fossil remains are principally of marine origin, but the remains of many amphibian and land animals, and often of birds, have frequently been imprisoned in an accumulating bed of sand or mud, as, for example, in a lake, or in the alluvium of a river, or along a sea or lake beach. We are thus afforded an absolutely truthful but unfortunately very meagre record of the evolution of the various types of life forms from the earliest times.

Now and then a bed of volcanic ash consolidated into hard rock is met with, or beds of infusorial earth formed from an aggregation on a sea bottom or lake bottom of the silicious remains of microscopic life forms (diatoms); but as these are rare, and as the latter appear to have been principally formed only in late geological times, the three classes of sediments above mentioned, which when consolidated are referred to as sandstones, shales, and limestones, may be broadly considered as comprising all of the sedimentary rocks.1

These sediments are nearly always commingled, and we have as a consequence sandy (arenaceous) shales and sandy limestones, shaly (argillaceous) sandstones and shaly limestones, calcareous sandstones and calcareous shales, sometimes referred to as marl beds. These names are applied to the strata formed by the deposits accordingly as the original sand, mud, or calcareous matter predominates. On the other hand, it is often remarkable how very distinct they are from each other, owing largely in all probability to the sorting effect of the water carrying the sediment,

1 It should be mentioned in passing that diatoms have the faculty of abstracting the silica from the sea water in much the same way as the coral and other kinds

of life forms have the faculty of abstracting the carbonate of lime out of which their shells are made.

and also to many unknown conditions surrounding their deposition. These sediments, as can be readily understood, were principally laid down at the mouths of rivers, or on the sea bottom near to the shore line. In the majority of cases it is certain that the deposition of the sediment proceeded with inconceivable slowness. In some cases, however, it is certain that these sediments were deposited far from the shore, as ocean currents would easily carry such finely divided sediments a long distance from the shore. The origin of some chalk beds is probably explained in this way.

After, and often before, being consolidated into hard rock (by pressure of superimposed sediments, and often by a cementing process due to the chemical action of some of the constituents of the deposited material, such as iron, lime, silica, etc., or by heat) these sediments have been raised and have become land areas. When consolidated, these form the ordinary stratified rocks with which all are familiar, and which form the greater part of the surface of the earth exposed to our examination. They are often found aggregating many thousands of feet in thickness. An individual bed of any of the kinds mentioned in such a series of stratified rocks may vary from a few inches or even a fraction of an inch to hundreds and, in rare cases, several thousands of feet in thickness. They, however, usually alternate constantly, owing to the differing conditions which produced them.

Familiar sections of Stratified Rocks (Geikie).1

In some cases, and especially when they are of great geological age, these beds or strata have been heated or baked and compressed to such an extent that they have lost their original character of sandstone, shale, and li nestone, and have become respectively quartzites, slate, and marble beds. This metamor

1 Many of the diagrams contained in this Preface are taken from well-known treatises on geological subjects. Others are from sketches by the author. All are

purposely made very simple in character, and are intended to render more clear the subjects discussed in the text.