ELEMENTS OF GEOLOGY. 



LESSON I. 



GSOLOGY DEFINED. Form of the Earth its Surface Internal 

 Heat Mineralogy defined Definition of the term Rock 

 Formations Strata The Origin of Strata Vegetable Earth 

 ~Allumum Division of the Formations Plutonic Forma 

 tions Neptunian or stratified Hocks Order of Strata Tern 

 pie of Jupiter Serapis Subsidence and Elevation of Coasts. 



1. GEO'LOGY (from the Greek, ge, the earth, and logos, dis- 

 course), or science of the earth, is that branch of Natural History 

 which treats of the physical constitution of our globe. 



2. The earth, as is generally known, is in form of a ball, or 

 spheroid, slightly flattened at the poles, floating freely in space. 

 Its diameter is about 8000 miles, and its surface is irregular ; here 

 it is studded with long chains of mountains, there hollowed by 

 deep depressions ; but these inequalities, however gigantic they 

 may appear, when compared with objects surrounding us, are in 

 reality very trifling, in comparison with the mass of the globe ; 

 they are proportionally much less than those we see on the skin 

 of the smoothest orange, and if represented on a ball three feet in 

 diameter, the highest mountains would be still so small as almost 

 to require a microscope to perceive them. 



3. The deepest excavations of the surface of the globe are 

 covered by great riasses of water which conceal them and prevent 

 their examination ; but there is reason to believe that the most pro- 

 found depression? do not much exceed three miles in depth, below 

 the surface of tb j sea, and we know by exact measurement that 

 the summit of tKe loftiest mountains is no.t six miles above the 

 same level. 



Mont Blanc, th^-s highest mountain in Europe, is 15,748 feet; Mont Perdu, 

 of the Pyrenees, is 11,168 feet; Peak of Teneriffe, 12,172 feet; in South 

 America, in the Cordillera of the Andes, there are still higher mountains, 



1. What is Ecology 1 



2. What ie the form of the earth 1 What is its size? What is the cha. 

 racter of its r urface 1 



3. What is the greatest depth of the sea 1 What is the greatest height 

 of land above the level of the sea ? 



