EXAMPLES OF GEOLOGICAL DESCRIPTIONS ' 97 



erly, in my opinion, under geography, because they give us good pictures 

 of land forms now existing. 



Finally, if in addition to statements concerning the rock structure of 

 the land-mass that is to be worked on, and concerning the erosive agents 

 that do the work, we add some indication of the amount of erosional work 

 that has been done by the working agent, and thus suggest a rather defi- 

 nite measure to the periods of past time that have been involved in the 

 production of existing land forms, then the geological quality of such a 

 description would become all the more pronounced, provided that men- 

 tion of structure to be worked on, of agencies that have done the work, 

 and of the stage of work reached by the agencies in their work on the 

 structural mass necessarily determine a description to be geological in- 

 stead of geographical. For example : Southern Xew England is chiefly 

 composed of disordered and for the most part resistant crystalline rocks, 

 with an irregularly defined north-south trend, which was long ago worn 

 down to a peneplain, save for a few scattered monadnocks of small relief ; 

 since then uplifted to its present altitude with a gentle slant to the south- 

 east, and after being for the most part maturely dissected by normal 

 agencies, recently strongly glaciated by an overwhelming ice-sheet and then 

 left in a slightly depressed position, so that the distal parts of its valleys 

 are somewhat drowned. Or, again, central England is occupied by a 

 heavy series of sedimentary strata, slanting gently to the southeast from 

 an irregular and deeply eroded oldland of complicated structure, the sedi- 

 mentary series including a first or basal member, a third or medial mem- 

 ber, and a fifth or uppermost member of relatively weak clays or marly 

 sandstones, and a second and a fourth member of relatively resistant 

 limestone or chalk, the whole region seeming now to be in a well advanced 

 stage of a second cycle of normal erosion, following the old age of a 

 pre\dous cycle, so that it possesses two well defined cuestas determined by 

 the resistant strata, separating an inner, a medial, and an outer lowland 

 eroded on the weak strata, all these features trending northeast-south- 

 west with the strike of the strata and drained for the most part by well 

 adjusted river systems. 



CLASSIFICATION OF THE SCIENCES 



Some students of earth science would regard brief descriptive phrases, 

 such as a maturely dissected landslide or an uplifted and slightly dis- 

 sected delta, as still in good measure geographical because of their sim- 

 plicity, while they would regard the descriptions of New England and of 

 old England, Just quoted, and still more the longer description of the 

 Colorado Front Eange, as geological because of their greater quantitv of 

 VII— Bull. Gbol. Soc. Am., Vol. 23, 1911 



