164 ROYAL SOCIETY OF CANADA 
These are amongst the most conspicuous and characteristie marine 
organisms. The Leda clay may best be examined at the St. Louis and 
Mile End quarries, at the Tanneries, and along the several terraces of 
Hochelaga and Montreal city, along Dorchester, Sherbrooke and other 
streets at different elevations, specially during excavations for building 
and other purposes. The Montreal formation (Saxicava sand) may be 
studied and examined at Mount Royal cemetery, and in the St. Louis 
and Mile End quarries. 
Recent Deposits —The St. Lawrence river, which during the “Cham- 
plain” period, deposited the Leda clay and Saxicava sands, was a 
wide sea or gulf with marine waters to a height of probably not 
less than 600 feet above its present level with direct connection with 
the Ottawa Valley to the west, is still carrying down towards the | 
Atlantic large quantities of detritus along its course and depositing the 
same, giving rise to alluvial.deposits. The Boucherville Islands, Sorel 
and Berthier flats, and the shores of the St. Lawrence adjoining, are all 
of recent origin and.the strata which constitute them consist for the 
most part of silts, gravels, sands, and the usual river mud deposits, 
holding fresh-water shells and plant remains of types precisely similar 
to those living in the immediate neighbourhood at the present day. 
These deposits vary from a few inches to several feet in thickness. In 
the chapter on Superficial Geology in his “Geology of Canada,” for 
1863, by Sir William Logan and his staff—a table of Pleistocene forma- 
tions and deposits is presented in which the St. Maurice and Sorel sands 
are given at the summit of what may be termed Meso-Pleistocene. The 
Sorel formation is an excellent term for the deposits in question. In 
the Eo-Pleistocene are included the Chaudière river gold-bearing gravels 
(Chaudière formation), and the glacial drift—here termed the Labrador 
formation—whilst the Champlain, Vermont, Beauport and Montreal, 
St. Maurice and Sorel formations follow. 
Of the Pleistocene formations about Montreal, the Leda clay affords 
excellent material for the manufacture of bricks and tiles and pottery, 
and the Montreal formation with its sands supplies materials used in con- 
struction. The limestones of the Black River and Trenton formations, 
besides affording excellent building stone, are valuable for cement pur- 
poses, and the sandstones of the Potsdam formation .might readily be 
usec. for blocks for pavement purposes. 
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