Page:Popular Science Monthly Volume 29.djvu/579

Rh value of our diplomatic representation there under Mr. Benjamin, we are informed that "it could not be otherwise than that the arrival (in June, 1883) at the capital of a legation of the United States should create in the mind of the Shah and of the officers of the Persian Government a greater interest in America and Americans. The missionaries were in a position to reap the benefits of this interest, and the minister, in the brief period of his residence in Teheran, was able to secure for them, from the Persians, some valuable concessions."

this work, as in the "Class-Book of Geology," by Archibald Geikie, noticed elsewhere in these pages, the plan pursued has been first to thoroughly acquaint the student with the various agents that effect geological changes, and their modes of action, and only then to pass on to the study of the different geological systems. The first half of the book is given to a careful investigation of the work performed by the different forces of Nature. This is discussed under two heads, viz.: "I. Epigene, or Superficial Action"; and, "II. Hypogene, or Plutonic Action."

The first of these divisions treats of the action of the atmosphere, of water, and of plants and animals, while the second studies the action of the subterranean forces.

The work done by terrestrial waters in effecting important changes receives due attention; rain, underground water, brooks and rivers, lakes, each is considered at length. Two chapters are devoted to the geological action of ice; another to the influence of the sea.

A review of the part performed by plants and animals in geological changes is followed by a chapter on the classification of the products of surface-action.

The second division, given to the consideration of subterranean action, embraces the subjects of volcanoes and volcanic products; the mineralogical composition of vitreous and crystalline igneous rocks; their penological character; movements of the earth's crust; the structure of rock-masses; ore-deposits, etc.

A chapter on paleontological geology forms the introduction to historical geology. The divisions here made are four in number: the primary or palæozoic, the secondary or mesozoic, the tertiary or cainozoic, and the quaternary or post-tertiary. Each of these is studied in turn. Numerous illustrations are given of the fossils occurring in and characteristic of the different periods. In fact, these illustrations, together with some others, inserted in the first part of the book, constitute one of the great attractions of this volume.

volume is intended to complete a series of educational works on physical geography and geology, projected by the author a number of years ago. It is a book written by the light of experience gained in practical teaching, and the writer's aim has been to produce a work that should awaken an interest in and love for the science of which it treats, and thus incite to original study and research.

The book is divided into four parts, and embraces a consideration of the materials for the history of the earth, a study of rocks, and how they tell the history of the earth, an account of the crust of the globe, and a careful analysis of the geological record of the history of the earth.

The influence of the atmosphere in changes affecting the surface of the earth, and the effects produced by water, under various conditions, take up the first few chapters. These are followed by an essay on "ice-records"—a history of the glacial epoch—and then comes an interesting description of how plants and animals inscribe their records in geological history.

In discussing the more important elements and minerals of the earth's crust, brief reference is made to the mode of occurrence, formation, and properties of each, and the crystalline form and the origin of crystallized minerals are carefully studied. Under the head of "The more important Rocks and Rock Structures" is