J. L. LOBLET — THE STUDY OF GEOLOGr. 177 



^itli matter in a state of fusion. This view is, however, opposed 

 by some of great knowledge and authority on this subject. But 

 whichever opinion we hold as to the character of the interior of the 

 earth, we may agree to call all that we can become acquainted with 

 by actual observation, "the crust of the earth." This is the term 

 which has been agreed to generally, although it was indubitably 

 first used to indicate that the interior of the globe consisted of a fluid 

 mass. We have therefore to deal with the crust of the earth, or, as 

 I before stated, with all that we can see of the structure of the 

 globe either at the surface or in excavations, mines, caves, or 

 fissures. Of the composition of the central parts of the earth we 

 can only at most infer, but of the composition of the crust of the 

 globe, we have abundant opportunities of observation. And 

 everywhere Ave find that this crust of the earth is composed of a 

 variety of hard rocks, either homogeneous or made up of several 

 distinct mineral substances, — of shales, of clays, of sands and 

 gravels, with great masses of water, containing various salts, filling 

 extensive depressions of the surface. 



I must now ask your attention to the word " rock." This word, 

 when used geologically, means any mineral mass forming a con- 

 siderable portion of the earth's crizst, whether hard or soft, 

 whether compact or disintegrated, whether granite, limestone, 

 sandstone, shale, clay, sand, or gravel. It may be used when 

 speaking of the softest bed of sand as correctly as when referring 

 to the hardest mass of granite. 



The whole earth may consequently be said to consist, as far as 

 we can discover by actual observation, of rocks and water. This 

 is what we find from ordinary general observation ; but when we 

 observe more closely, and examine the rocks in detail, we find that 

 they may be divided into two kinds by a very remarkable diiference 

 in their structure. We see that many of the rocks have a structure 

 which is called stratified, that is, they are found to consist of 

 layers, or parallel beds, or strata. These rocks are therefore 

 called stratified rocks. But all rocks are not so ; some we find 

 devoid of any indication of stratified arrangement. These, 

 therefore, we call un stratified rocks. All rocks are hence classed 

 in two grand divisions, the stratified rocks and the unstratified 

 rocks. The stratified and unstratified rocks form, with the water, 

 all the globe that it is possible for man to observe. The rocks 

 extend over the whole globe, but the water .over only a portion, 

 and always reposing upon and covering the rocks. The rocks un- 

 covered by the water we call land, and the water we call sea. 

 But the land and the sea are not in regular-shaped or compact 

 masses ; they are intermingled in an apparently most complicated 

 manner, the land assuming a great variety of forms seldom regular, 

 and the sea occupying the inter-terrestrial spaces. The study of 

 the various poi'tions of the land and sea is included in Geography, 

 but the study of the relation of Geology to Geography, or the 

 geological character and origin of the physical features of the 

 earth's surface, is Physiographic Geology. This portion of our 



