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be unstratified, because they are not arranged in layers. On the other hand the rocks which have been formed by the deposition of the worn fragments of the original surface are said to be stratified, because they are arranged in layers, like a pile of boards. They have all been formed under water; either fresh water or marine. Many of the layers or strata are subdivided into very thin plates like the leaves of a book, which are called lamina. Slaty rocks. are often traversed by divisional planes resembling laminæ, called cleavage planes, because the slates naturally cleave in the direction of these planes. Frequently the cleavage planes coincide with the laminæ. Another class of divisional planes called joints cross the strata in different directions and divide them into rhomboidal masses, parallelograms and cubes. The unstratified rocks are traversed by joints. Cleavage planes and joints are called superinduced structures because they have been developed by chemical forces since the original production of the rock.

Clay, sand, gravel and calcareous deposits, (such as are produced from mineral springs,) are the original forms of most of the stratified rocks. By various agencies these materials become consolidated into slates, sandstones, conglomerates and limestones; so that the newer rocks are generally more friable and less compact than the older rocks. The slates, sandstones, etc., which have been formed under similar circumstances during one geological period, and contain relics of the animals and plants living during that period, are called a formation.

The strata composing the different formations were originally horizontal. Now an examination of the strata along a given line, or a geological section, shows that the stratified rocks are tilted up at various angles, and that some layers have been forced up so as to stand upon their edges. Some great force in nature seems to have been at work gradually for ages, pushing the strata into great curves, of which the strata we examine in a section are parts. Hence it is easy to see how one is enabled to examine the oldest stratified rocks and all that have been formed since the earliest period. One formation has been elevated so that the character of its layers can be ascertained at the surface, and the formations which have been deposited since lie upon the older formation without concealing it entirely from view. Had there been no disturbances of the earth's crust, and had the formations encircled the earth one over another, like the concentric coats of an onion, it would

have been impossible to examine the oldest formation without excavating a passage through all the layers above it. Occasionally one formation has been elevated or tilted up before the formation immediately succeeding has been deposited. In such case the strata beneath are said to underlie unconformably the strata above with a less inclination.

Fossiliferous and Unfossiliferous Rocks.

A

An easy and natural division of the stratified rocks is into those which contain evidences of organic life and those without fossils or the fossiliferous and unfossiliferous or Azoic rocks. fossil may be defined as any relic or trace of an animal or plant buried naturally in the earth. In general, the unfossiliferous rocks are the oldest, of immense thickness, but not so thick as the ten or twelve miles of fossiliferous rocks overlying them.

Paleontology is the science of fossils or organic remains. From the study of fossils the following general statements have been deduced.

1. The whole number of species of animals and plants found fossil and described amounts to at least 35,000, of which 2,750 are plants.

2. Each formation is characterized by its peculiar group of fossils not found in any other, so that a paleontologist on seeing a specimen can usually tell from what part of the series it came.

3. The fossil species in Maine and the northern parts of the continent correspond more nearly to animals now living in the tropics, than to those now living in the colder climates. Hence the climate of even the Arctic zone must once have been tropical.

4. There have been at least six entirely different races of animals and plants upon the globe; and some authors estimate as many as twenty-seven life periods. Each economy of life seems to have entirely disappeared before the appearance of the succeeding race, and each successive group must have been introduced, as was the first one, by the action of an intelligent creator.

5. There are no animals now existing at all similar to many of the strange forms peopling the Preadamic world.

6. The successive groups of animals and plants are each more perfect than the one preceding: and the last group, or those now living, embraces the highest types of the animal and vegetable kingdoms.

Classification of Rocks.

The fossiliferous rocks may be divided into three great systems, according to the times when the successive economies flourished: 1. The Paleozoic system of life, or the ancient—the oldest-types of being: 2. The Mesozoic system of life, or the types that flourished during the middle periods of organic life nozoic system of life, or the recent types of life. general divisions. The subdivision of strata has now been carried to great nicety.

and 3. The CaiThese are only

A formation in America is identified with the corresponding strata in Europe by means of the organic remains characteristic of that group. Previously the European strata had been examined, and had received a local name, giving it a definite place upon the series. For example, one of the lowest formations of the Paleozoic system was first explored in Wales. Hence it was called Silurian, (from an ancient name of the country.) Now when strata of the same age are found in America they are termed Silurian, i. e. strata of the same age with those in Siluria. The term Silurian is yet a general one. It has been subdivided into thirteen parts in England, and into sixteen in North America, each being named from the town or region where it is best developed.

The unfossiliferous stratified rocks, as well as the unstratified, are at present classified according to their lithological structure. We present here a tabular view of all the stratified and unstratified rocks, arranging the former in the order of their age, mentioning the most recent first.

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B.-UNSTRATIFIED OR IGNEOUS ROCKS.

I. GRANITIC GROUP.

1. Granite. 2. Syenite. 3. Protogine.

II. TRAPPEAN GROUP.

1. Porphyry. 2. Greenstone. 3. Amygdaloid, etc.

III.-VOLCANIC KOCKS.

1. Bassalt. 2. Trachyte. 3. Pumice. 4. Tufa. 5. Peperino. Ashes. 7. Vesicular lava, etc.

6. Volcanic

The fossiliferous rocks of Maine are mostly Paleozoic, and probably below the Carboniferous series. The rest belong to the Alluvium. Probably the subdivisions of the Paleozoic rocks in Maine will correspond neither with the subdivisions of these rocks in England nor with those west of the Green Mountain range. As there will be constant references to these subdivisions elsewhere, both in this report, and in the future progress of the examination of the rocks of Maine, we will give in a table their names as used in England and North America. Much labor must be spent in ascertaining how near the subdivisions of the Paleozoic rocks of Maine correspond with the others. At present it is impossible to compare them because the thickness and extent of these rocks in Maine are not known.

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The Carboniferous system of this country is from 6,500 to 14,500 feet thick. The Devonian rocks are 11,950 feet thick. The Upper Silurian rocks are about 4,800 feet thick. The Lower Silurian rocks are estimated from 1,800 to 8,500 feet in thickness. The Huronian rocks are 12,000 feet in thickness.

Metamorphism.

The rocks originally deposited were mostly sandstones, shales, conglomerates and limestones. But many of them have undergone great alteration in their physical characters since their production. Heat, water and chemical forces with various degrees of intensity have been converting many sedimentary rocks into crystalline masses, so that often the original features of the formation are entirely obliterated. The pebbles may disappear or be so distorted as not to be recognizable; shales become slates; fossils are obscured; and often a superinduced structure becomes far more prominent than the original planes of stratification. This transformation of rocks from one kind to another is called metamorphism.

Denudation and deposition accumulate together a mass of heterogeneous materials, mixed together without reference to a chemical arrangement of the particles. The process of metamorphism consists analytically of two parts: first, the production of the conditions in which chemical forces can act, and secondly, the action of these chemical forces. The conditions favorable to the development of the forces are plasticity of the materials in connection with the presence of warm water or steam. Under these circumstances the laws of chemical affinity cause the different elements to form such new combinations as the conditions require. Sometimes a portion of the ingredients of the sedimentary rock are removed in this change, leaving the other ingredients only to form the altered rock. The results become somewhat complicated when new ingredients are introduced into the sedimentary rocks, held in solution by the water diffused through the plastic materials. We suppose that the greater amount of metamorphism is produced by the latter method.

Many metamorphic rocks are foliated. Foliation is a change in metamorphic rocks analagous to cleavage. It is a crystalline lamination, or a separation of the different mineralogical compounds into distinct layers much resembling strata. Generally the foliated

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