240 VOCABULARY. 



GEOI/OGY is that branch of natural science which treats of the 

 structure of the crust of the earth and the mode of formation 

 of its rocks, together with the history of physical changes 

 and of life on our planet during the successive stages of its 

 history. It has been inferred that its actual crust must be 

 very thick, perhaps not less than 2,500 miles. Geology de- 

 pends upon mineralogy for its knowledge of the constituents 

 of rocks, and upon chemistry and physics for its knowledge 

 of the laws of change ; and in its study of fossil remains it is 

 closely connected with the sciences of zoology and botany. 

 A knowledge of geology lies at the base of physical geogra- 

 phy, and is essential to the skillful prosecution of mining 

 and other useful arts. J. W. Dawson. 



The facts proved by geology are that during an immense 

 but unknown period the surface of the earth has undergone 

 successive changes ; land has sunk beneath the ocean, while 

 fresh land has risen up from it ; mountain chains have been 

 elevated ; islands have been formed into continents, and con- 

 tinents submerged till they have become islands ; and these 

 changes have taken place, not once merely, but perhaps 

 hundreds, perhaps thousands of times. A. L. Wallace. 



Prof. Dana says the " earth was first a featureless globe of 

 fire ; then had its oceans and dry land ; in course of time re- 

 ceived mountains and rivgrs, and finally all those diversities 

 of surface which now characterize it." 



GLAND. (An acorn ; a kernel.) Softish, granular, lobated or- 

 gans, composed of vessels and a particular texture, which 

 draw from the blood the molecules necessary for the forma- 

 tion of new fluids, conveying them externally by means of 

 one or more excretory ducts. Each gland has an organiza- 

 tion peculiar to it, but we know not the intimate nature of 

 the glandular texture. 



GUANA'CO. The ' Auchenia Huanaca,' a species of the genus of 

 ruminant mammals to which the llama belongs. It inhabits 

 the Andes, and is domesticated. It is allied to the camel. 



Webster. 



The guanaco is especially abundant in Patagonia and 

 Chili, where it forms large flocks. It is about three feet high 

 at the shoulders, and is extremely swift. In domestication it 

 is ill-tempered, and has a disagreeable habit of ejecting saliva 



