Fig. 72. THE SALSES, OR MUD VOLCANOES, OF CARTHAGENA. 



THE CRUST OF THE EARTH ; 



OR, FIRST NOTIONS OF GEOLOGY. 

 CHAPTER VI. 



1 53. Form of craters. 154. Stromboli Formation of internal adventitious 

 cones and craters. 155. Strata of lava how formed. 156. Formation 

 of lava ndykes. 157. Salses, or mud volcanoes. 158. Fumarolles. 

 159. Geysers. 160. Valleys of elevation. 161. Formation of parallel 

 ridges. 162. Slow operation of air, water, and heat. 163. Atmos- 

 pheric effects upon rocks. 164. Effects of water on rocks. 165. 

 Effects of the sea on cliffs. 166. Effects of waterfalls. 167. 

 Effects of the sea and of icebergs on the forms of rocks. 168. Geo- 

 logical phenomena explicable by natural causes still in operation. 169. 

 Portland dirt-bed Its organic deposits. 170. Climate of England 

 tropical at the epoch of these deposits. 171. Example of coal deposits. 

 172. Northumberland coal mines. 173. Colliery near Wolver- 

 hampton. 174. Deposits in Treuille mine at St. Etienne. 175. 

 The character of the waters shown by the organic deposits Fossil 

 shells. 



153. IT has been impossible to obtain direct observations of the 

 interior of craters when in a state of active eruption, but when 

 they have been approached immediately after the cessation of an 



LA RISER'S MUSEUM OF SCIENCE. i 113 



No. 141. 



