REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1903 25 



In some oases the floating bog becomes heavier than the water 

 and " either breaks and sinks suddenly to the bottom or is slowly 

 and gradually lowered into it and covered with water ."^ Authentic 

 instances of such sinking are rare; but about the year 1500 a 

 forest in the Valdes-Ponts sank in one night, giving place to the 

 Lac d'Etaill^res. In this way most, if not all, of the submerged 

 forests have probably been formed and brought to their present 

 position, and it is the most logical explanation that can be given 

 for the alternation of peat and marl in many swamps. 



River swamps. Terrace swamps are in certain respects merely 

 modifications of lake swamps and are formed in depressions in 

 river valleys. These depressions are caused in a great measure 

 by the deposition of sediment near the river bank in time of high 

 water, thus forming a dike which prevents any water which may 

 overflow from the river from again returning to the watercourse 

 when the flood recedes. The pools formed in this way become 

 more or less covered with swamp vegetation and in time are filled 

 with a deposit of impure peat and muck. The oxbows or moats 

 of a river system, when cut off from the river, form pools which 

 fill up in the same manner as a lake, though floods leave deposits 

 of mud on the surface of the vegetation, thus forming a more 

 mixed deposit than is formed in a true lake, where little sediment 

 can reach the still water beneath the floating vegetation, and none 

 at all can go above it. 



Delta or estuarine swamps. The dikes or levees formed by a 

 river naturally extend to its mouth and are gradually extended 

 beyond the shore line. In many cases the river breaks through 

 this wall and may have several outlets, thus forming a delta. The 

 space between these outlets is usually lower than the banks of 

 the river, and swamp vegetation springs up and a delta swamp is 

 the result. In case this delta is at the head of a lake, the grada- 

 tion from the delta formation to the lake margin swamp may 

 be so gradual as to make it difficult to tell where the line of 

 division should come. True delta swamps are not common in 



^Lesquereaux, L. Pa. Geol. Sur. An. Rep't. 1885. p.107-8. 



