GULLIVER, — SHORELINE TOPOGRAPHY. 187 



abandoned its former stand on account of the removal of its barrier or 

 dowu-cuttiiig of its outlet, is in the topographic sense as truly an elevated 

 former shoreline as if the land had been raised. The relative position 

 of land and water is changed. 



Typical forms of Bonneville. — Many of the illustrations of shore forms 

 of the Bonneville, Provo, and levels intermediate iu position between 

 lake Bonneville and Great Salt lake serve as types of elevated former 

 shorelines, in youthful stages. The deltas, terraces, embankments, clifFs, 

 V-bars, bay-bars, and the tying of islands to the mainland are all charac- 

 teristically shown. The stratigraphic and paleontologic proof of the 

 relative age of the shorelines is brought out by Mr. Gilbert, but the 

 fading features of the older shorelines are not dwelt upon to show 

 relative ages. 



Lake Agassiz. — The descriptions of the shore forms of the ice-dammed 

 glacial lake Agassiz are given iu this same manner, as if the forms were 

 formed once for all and would forever remain as constructed. Gen. G. 

 K. Warren set aside the hypothesis of an ice-barrier and argued for an 

 actual change of level, depression to the south accompanied by a rise to 

 the north. Mr. Upham has traced the various beaches formed by the 

 different water levels and shown them to have been the result of an ice 

 mass to the north gradually retreating toward Hudson bay. These ele- 

 vated former shorelines rise from south to north and from west to east, 

 in the direction of the former ice-fields, the amount of slope varying from 

 zero to one and one third foot per mile. Since these old shores must 

 have been horizontal when formed, their present position shows a tilting 

 since the time of lake Agassiz. 



Marine and Lake Terraces. — Early writers used the beach form to show 

 elevation,* but they often did not distinguish between the seashore forms 

 and those which had been produced by water above the sealevel. One 

 of the most fruitful sources of error has been in regarding the terraces 

 of ice-dammed lakes as produced by marine action. The classical exam- 

 ple is that of the Lochaber terraces, the Parallel Roads of Glen Roy. 

 For an historical discussion of the change of view from tiie detrital 

 dammed lake to the action of the sea and finally to the present hypoth- 

 esis of an ice-dammed lake, see " The Great Ice Age," by Professor 

 Geikie. t The geographic criteria for the differentiation of the similar 

 forms produced by these two processes are these. At the level of the 



* R. Chambers, 1847, and many later writers. 

 t 3d ed., 1895, 282-285. 



