INTRODUCTION

TO TIIB

STUDY OF GEOLOGY.

Section i. General Remarks.

1. Modern geology constitutes a very interesting brand) of na--tural science. Its object is to ascertain the arrangement and mutualactions of the solid, fluid, and aeriform materials of the earth. Toeffect this object, it investigates the structure, position, direction, andrelative situation of those large masses, beds, strata, and veins of miner-als, vvhicli compose the exterior crust of this globe. Its researchesextend also to the various alterations and decompositions, to whichthe mineral kingdom is subjected by the action of air, fire, and wa-ter. These changes may be gradual and slow, or violent and sud-den. They are in part effected by rains, floods, tides, by lakesbursting their bounds, by the depression of land near seas, by the fallof mountains, by ear thquakes, volcanic eruptions, &c.*

2. The study of geology cannot be pursued in the cabinet. It isnot the structure of a single specimen nor of a whole rock, that mustbe observed ; the examination must extend to the structure and re-lations of whole mountains and even chains of mountains. Thisstudy embraces a vast number of facts, extremely diversified in theirnature, complicate, and often very difficult to investigate.—Henceone source of the various geological systems, which have been pro-posed. Ilence also, it is obvious, that numerous and extensive ob-servations must be collected, before any general principles can be de-duced and received with confidence.

3. Some of the obstacles to geological investigations arise fromthe interruption or mutual intersection of the strata, and from thedifficulty of determining the nature of certain rocks. Others pro-ceed from the gradual disintegration of minerals ; or from the morepowerful action of torrents, earthquakes, and subterraneous fires,

* See an enumeration of several important and extensive changes, produc-ed by some of the above mentioned causes, Jameson’s Mineralogy, v. iii.