71 



.1. W. SPENCEB — A.NCIENT SHORE PHENOMENA. 



beaches, atul the finer clay, that which constitutes the off-shore silt deposits* 

 leveling up the inequalities of the lake bottom and forming very flat Bub- 

 merged plains, which are rendered apparent upon the withdrawal of the 

 waters. 



In the examination of old shores, the occurrence of flat or very gently 

 inclining plains, abutting at constant levels against rising hills is as certain 

 an indication of old coast-lines as if beaches were found there; but the 

 exact height of the water-line cannot be recognized, as the water may have 

 been five or it may have been twenty feet deep. When this condition 

 obtain.-, there may remain here and there a fragment of a temporary beach 

 (e, fig. 4), covered by a landslide (*, fig. 4), but exposed by a stream or arti- 

 ficial cutting into the hillside, or there may be a barrier in front of an 

 ancient bay or lagoon (h, fig. 5). 



Whilst the greater proportion of the lake coast is composed of drift 

 deposits, there are places where the water-margins are bounded by rocks. 

 Here the structure is similar, although not so well developed, and the banks 

 may assume the form of vertical cliffs. Generally speaking, the beaches in 



Fioubi 5.— Map of tht Wt I I io. 



; Burlington beaoh, separating Burlington bay from the Lake, h Burlington h< 

 i 108-116 feet high, si-parating Dund.-i* marsh from Burlington bay. 



front of tin se rocks are not bo well developed as where there haw been Bhore 

 deposits of boulder clay to supply the wave- with pebbles. However, some 

 of the higher and older coast-markings remain in the form of such "sea- 

 cliffs," in front of which there are compa rat ively fiat plains. 



Another structure, when present, is very characteristic of many portions 



of the ancient shores, or, indeed, is occasionally Been in front of the i lern 



beaches. This is a pavement of boulders (derived from adjacent Bhores of 

 boulder claj , occupying a given /one (P, figs 2 and 3). This /one i- in 

 front of and a few feet lower than the level of the true beach ; the bouldi rs 

 baving been left just below the water-level as the wave- made encroachments 

 upon the coast. Again, the boulder- have been more or less pushed up to 



