65 



liglit yell owish-g rev sandstones, xinderlaid by dark bluish green aren- 

 aceous sliale'i of a rather brittle nature. The rapids here doubtless owe 

 their origin to these softer shales, which have been denuded and washed 

 down the river. A few fossils were found in a stratum of rock which 

 was ferruginous. The beds are almost horizontal, dipping very slightly 

 to tlie west, and extend quite a distance west, south and east of this 

 •exposure, being well exposed at A.ylmer and Britannia, as well as at 

 Skead's Mill, where there is a quarry of building stone from which 

 many of the finest edifices in Ottawa hive been partially or wholly 

 built. 



II. Another interesting exposure of this formation, doubtless con- 

 nected with that just described, occurs on the south-western shore of 

 McKay's Lake, New Edinburgh, the strata here being but little superior 

 stratigraphically to those at Des Chenes. This is brought to sight by 

 an extensive fault running in an easterly direction across the measures 

 of the Cambro-Silurian formations here, and referred to in the Geology 

 of Canada, 1863, a downthrow on the north side of the fault being 

 clearly shown. Altogether, the beds form a thickness of some 20 feet, 

 and appear quite destitute of fossils ; the upper measures consist of a 

 very brittle series of gre.enish-grey argillaceous shales which cleave at 

 all angles and disintegrate to some extent. This exposure is part of one 

 of two anticlinals, the other being at Hog's Back, in Nepean, Ont. , 

 while in the synclinal basin between them are comprised the Black 

 River, Trenton and XJtica formations, together with the Pliocene and 

 drift deposits. 



III. The summit of the anticlinal at Hog's Back, Nepean, has been 

 denuded and broken, a fault of several feet — again a downthrow on the 

 north-eastern side of the fault — occupying the place where the rocks 

 were rent. Here the sandstones predominate, and but very few shales 

 occur. The hard quartzose beds pass from areiio-argillaceous shales to 

 calcareous sandstones, whilst the latter are immediately overlaid by 

 limestones holding numerous fossil organisms. A band of the most 

 argillaceous sandy beds yielded great numbers of the typical species 

 Lingula Belli, (Billings), also an abundance of a lamellibranchiate 

 mollusca, which may prove very interesting to palaeontologists, as 



