167. Longitudinal sections of upper portion of a river valley 161 168. Map and sections of a stream meander 163 169. Tree undermined on the outer bank of a meander 164 170. Diagrams to show the successive positions of stream meanders 164 171. An ox-bow lake in the flood plain of a river 165 172. Schematic representation of a series of river terraces 165 173. “Bird-foot” delta of the Mississippi River 167 174. Diagrams to show the nature of delta deposits as exhibited in sections 168 175. Gorge of the River Rhine near St. Goars 169 176. Valley with rounded shoulders characteristic of the stage of adolescence 170 177. View of a maturely dissected upland 170 178. Hogarth’s line of beauty 171 179. View of the oldland of New England, with Mount Monadnock rising in the distance 171 180. Comparison of the cross sections of river valleys of different stages 172 181. The Beavertail Bend of the Yakima River 173 182. A rejuvenated river valley 174 183. Plan of a river narrows 174 184. Successive diagrams to illustrate the origin of “trellis drainage” 175 185. Sketch maps to show the earlier and present drainage near Harper’s Ferry 176 186. Section to illustrate the history of Snickers Gap 177 187. Character profiles of landscapes shaped by stream erosion in humid climates 177 188. Diagram to show the seasonal range in the position of the water table 180 189. Diagram to show the effect of an impervious layer upon the descending water 181 190. Sketch map to illustrate corrosion of limestone along two series of vertical joints 181 191. Diagram to show the relation of limestone caverns to the river system of the district 182 192. Plan of a portion of Mammoth Cave, Kentucky 183 193. Trees and shrubs growing upon the bottoms of limestone sinks 183 194. Diagrams to show the manner of formation of stalactites and stalagmites 185 195. Sinter formations in the Luray caverns 186 196. Map of the dolines of the Karst region 187 197. Cross section of a doline formed by inbreak 187