126 



J. W. SPENCEE ON 



St. Lawrence Eiyer, and must have had a depth of from 680 to 800 ' feet, in place of 

 from 120 to 240 feet of the present day. 



(5.) Characteristics of the Beach. — In form, most typical and easily followed, 

 especially in Canada, the beach consists of a coastal barrier (fig. 4, b' and fig. 5 a), behind 



Fig. 4.— Horizontal plan of a barrier beach (?/) in front 

 of a lagoon, back of wliich there are coastal hills. 



î^iG. 5. — Vertical section of ancient beaches in différ- 

 ent forms {a,h,c,) with outlying sand bar {d). I)', 

 former surface of water. 



which there are depressions, once filled by the waters of some swamp or lagoon. The 

 barriers often pass into spits and bars, and cross old valleys. Again the barriers give 

 place to terraces of construction, (fig. 6 a). The material is invariably gravel, rich in 

 sand, well stratified, but often showing false bedding, of various forms. At both the 

 eastern and western ends of the lake, there may be seen three distinct ridges (fig. 5 b) 

 with a maximum difference in height of about 25 feet at the eastern end, and somewhat 

 less at the western. But these ridges commonly run together, and form one or two crests, 

 or may be furrowed into a dozen (fig. 5 c) . The face of the beach slopes gently to the 

 the subaqueous coastal plain, descending five, ten, or even twenty feet (when all the 

 ridges are united into one). 



The depressions behind the barriers are much more abrupt, and the slopes greater 

 than in front. Following the beach, it is only at occasional capes that the surface does 

 not appear level, and then the variation is due to the waves that were exceptionally high. 

 Ordinarily I should not place the water margin more than five feet below the tops of 

 the ridges, and usually less — rarely ten. There are several transverse sections cut through 

 the ridge (or combined ridges) which, when best developed, measure 500 to 600 feet across. 

 The depth of this beach deposit, upon clay beds, is ordinarily from twelve to fifteen feet 

 thick, except in the spits, where it even reaches to a hundred feet or more. The beach 

 may be upon or against the shore bank, or at some distance lakeward, but in front of it, 

 there is invariably a great broad plain from hundreds to thousands of yards wide. The 

 plain is usually covered with a lake-deposit of silt which forms the best soil in the 

 region. But upon it, at some distance lakeward of the beach, there is commonly found a 

 sand ridge (fig. 5 d), representing the fine deposits borne outward by the undertow 

 of the sorting waves. The plain is the floor of the cut terrace, typically bordered by the 

 gravel beach in front of the higher shores. 



The beach itself is often wanting (fig. *7) for distances of a few hundred yards or even 

 a few miles, but it may be replaced by rows or pavements of boulders. However, it is 



' 120-240 ft.— 120 feet being depth of modern soundings in channel, excavated out of limestone below King.ston, 

 and 240 being depth of channel excavated out of Laurentian rocks, at a point north of Cape Rutland ; 450 ft., 

 height of beach above river at Cape Rutland, plus 110 ft., the calculated increased elevation of water-level above 

 the river between Cape Rutland and the places of sounding. 



