FOKMEE HEIGHT OF SEA. 483 



5. The deeper interior valleys now occupied by streams and ri^^ers. 

 The main valleys are often connected by cross or transverse valleys or low 

 passes. Up to the highest level of the sea we should expect these trans- 

 verse valleys to have been occupied by straits forming- a complex system of 

 reticulating channels surrounding numerous islands. A corresponding series 

 of sands and clays would mai'k these old channels, or straits. Up to the 

 height of these transverse plains of fine sediments it is at least possible that 

 the sea extended. Yet it is also possible that the floods of rivers might 

 rise above the divides between neighboring valleys, and thus an overflow 

 might take place from one to the other. It thus becomes necessary to dis- 

 tinguish a possible form of valley drift from marine beds before it becomes 

 certain whether the transverse plains of fine sediments mark the presence of 

 the sea. 



6. The character and structure of the sediments. This constitutes 

 another method of distinguishing between the valley drift and the marine 

 beds. Into the main marine bays of the time when the sea stood at its 

 highest level poured large rivers which to the north were fed b}' waters of 

 the melting ice-sheet. Above sea level they were depositing valley drift; 

 within the sea, flu viatile marine deltas. Estuarine deposits would form the 

 transition between the two. The determination of the points of transition 

 would be rendered difficult by the rise and fall of the tides, and especiall}^ 

 by any general rise or fall of the sea level whereby at successive periods 

 the fresh and salt waters met at different places. If we should find a great 

 change in the coarseness of tlie sediments taking place Avithin narrow 

 vertical limits, proving considerable slowing of the waters at that j^oint, 

 and especially if this were observed in several valleys at the same relative 

 position to the lines of highest elevation as determined by observation 

 of the coast beaches, we should have probable proof that the streams of 

 the laiid poured into the sea at those points. Thus far I have not been 

 able to apply the method satisfactorily, in part owing to the raritv of 

 known elevations in these valleys. "Where the streams were large com- 

 pared to the breadth of the valleys it is doubtful if this method can be 

 applied with certainty. The broader and shorter valleys, off the lines 

 of the glacial rivers, are the most promising eases for the application of 

 the method. 



The following data give approximate elevations of the higliest shore in 



