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The Ottawa Naturalist 



[Vol. XXXII. 



of the glaciers from the region, are comparable with 

 those of the Bay of Fundy, where the strand line is 

 generally defined by the margins of broad nearly flat 

 stretches of sand or mud. Across these broad 

 intertidal belts the sea in many places retreats for 

 miles at the turn of the tide, leaving nothing to 

 mark its maximum landward extent beyond the 

 margin of the tide-borne sand or mud. 



Here and there in the Ottawa valley, where they 

 have escaped erosion, we find vestiges of the old sea 

 beaches and the life which flourished on them. 

 Southwest of Ottawa, six miles, the Rideau river 

 has cut into one of these old Pleistocene beaches at 

 a locality a few hundred yards below the Black 

 rapids. The work of the river, combined with the 

 extensive excavation of sand for use in the City of 

 Ottawa, has furnished an excellent section of the 



referred to as representing a sea beach of yesterday. 



The face of the sand pit, which is kept nearly 

 vertical by constant removal of sand, exposes about 

 60 feet of clean quartz sand. The sand furnishes in 

 its cross bedding evidence of the wave and current 

 action which characterizes most beach deposits, 

 (fig. I). From the top of the pit the surface of the 

 sand stretches away toward the east as an approxi- 

 mately level surface. Except for slight irregulari- 

 ties represented by a few low dunes and a very 

 moderate amount of reduction by erosion, the surface 

 of this sand plain shows about the same topographic 

 contour which it had as a beach or bar in the 

 shallow waters of the Pleistocene sea. 



The location of Ottawa, more than 200 miles 

 from the nearest salt water, in a region where lakes 

 are common, might lead the intelligent layman to 



Fig 1. Face ol ^aiid iiil, near Kiileau .Junelioii, (Jul. These sands 

 represent a shallow water deposit of the Champlain sea. 



old beach sands (fig. 1). The removal of this old 

 beach deposit by the river began immediately after 

 the birth of the Rideau and Ottawa rivers, an event 

 which followed directly on the retreat of the sea 

 from the region. This surviving remnant of the old 

 beach can therefore give but an imperfect concep- 

 tion of the original extent and outline of the old sea 

 shore. 



If the visitor to this interesting locality should 

 approach it by way of the charming canoe route up 

 the Rideau canal and river he will pass, at the 

 picturesque Hogs Back rapids, extensive exposures 

 of Ordovician limestone, the prcduct of another 

 long extinct sea which compares in age with the 

 sand pit deposits very much as the Pyramids do 

 with the Ottawa Union station. In contrast with 

 the limestones of the Ordovician, whose age we 

 estimate in millions instead of thousands of years, 

 the sands of the Rideau pits may with propriety be 



enquire what evidence there is for calling this deposit 

 of clean washed sand a sea deposit rather than a 

 lake beach formation. And if it is of marine origin, 

 he may ask what proof can be offered of the shallow 

 water origin which its reference to a sea beach 

 implies. The answer to both of these questions is 

 found in the fossil fauna which the sand beds hold. 

 THE fauna. 



Some of the upper beds of the sand pit hold a 

 great abundance of marine shells. All of these 

 belong to species now living in the Gulf of St. 

 Lawrence and thus attest the comparatively recent 

 withdrawal of the sea from the Ottawa river valley, 

 (fig. 2). The following species have been collected 

 by the writer: Mylilus edulus, Macoma bathica, 

 Saxicava rugosa, Balanus sp. 



Perhaps the most interesting and significant species 

 in this list is Mylilus edulus. The shell is abundant 

 nearly everywhere on our present Atlantic coast, at 



I 



