OUTLINES OF GEOLOGY. 



9 



tions of the ocean of much greater extent of surface than 

 the lands we have mentioned. The opposite hemisphere 

 being brought up, the two great islands will be seen, separated 

 by a channel of small extent when compared with the 

 residue of the ocean. This channel is the North and South 

 Atlantic ; it is widest between the southern extremities of 

 Africa and South America, and although irregular, gradually 

 decreases in width, until, having passed the north pole, it 

 communicates with that part of the great ocean known as the 

 Pacific, through Behrings Straits. 



14. Besides the main ocean and this great arm, both have 

 numerous branches, which go by the name of seas, gulfs, 

 and bays. The most important of these are the Mediterra- 

 nean, Baltic, and Carribean seas. 



15. The continents also enclose large masses of water 

 which are called lakes, or even, when of great extent, al- 

 though improperly, seas. On the old continent, the most 

 extensive of these is the Caspian, and on the new, Lake 

 Superior. Some of these lakes communicate with the ocean 

 by channels, through which their surplus waters are dis- 

 charged into its basin as a common reservoir. Others have 

 no outlet. All lakes which have outlets contain fresh water 

 alone ; those which have no outlet are salt. 



16. The channels by which the surface waters of the land 

 are carried into the ocean are called rivers. These differ 

 extremely from each other in size ; those which are smallest 

 are styled rivulets or brooks ; in America those of mean 

 dimensions are usually called creeks, which, although not the 

 legitimate application of the term, is, notwithstanding, conve- 

 nient, as a term is obviously wanted to distinguish such 

 streams as the Mississippi and Amazons, from those of no 

 more extent than the Thames or the Seine, 



