190 The Ottawa Naturalist. [Feb. 



section of the entire thickness. In order to get an idea of the 

 whole formation, it is, therefore, necessary to measure the rocks 

 exposed at each favorable outcrop, and correlate the various 

 sections. Fortunately there are a few beds which may easily 

 be recognized by their lithology and fossils. One of the most 

 useful of these beds is a very black thin-bedded shale containing 

 Isochilinaf clavigera, a. large and easily recognized ostracod. This 

 bed is exposed opposite Mr. Sowter's house on Broad Street, 

 Aylmer, beside the electric railway one mile west of Westboro, 

 near the ruins of Skead's Mill, and was revealed in a trench 

 on Buena Vista Road, at the corner of Minto Place, RockclifEe, 

 during excavations made this last summer. A second horizon 

 is indicated by thin-bedded limestone containing Onchometopus 

 simplex, and always followed by a layer full of a species of 

 Beatricea. This horizon was found at Aylmer, Mechanicsville, 

 and on a road leading to the river from a point just east of 

 Robilliard's quarries on the Montreal Road. A few other easily 

 recognized beds have been found useful in checking up the 

 correlations made on the basis of the two just described. 



Sections. 



The lower portion of the formation is best displayed at 

 Rockcliffe, where the following section was measured, the beds 

 being given in descending order : 



Ft. Ft. 



4. Green shale with numerous Lingulcp 5 5 



3. Heavy-bedded, light gray sandstone 10 15 



2. Rather heavy-bedded light gray sandstone with 

 some cross-bedding, and thin layers of coarse 

 grains of sand. Camarotcechia plena and 

 Hebertella imperator at the base 10 25 



1. Shaly, thin-bedded, light colored sandstone with 

 lenses of heavy-bedded sandstone. Rusophy- 

 cus grenillensis and other burrows and trails 

 are common 53 78 



At this locality the base of the black layer with Isochilinaf 

 clavigera is about 31 feet above the top of this section. A large 

 part of the intervening strata are concealed here, but are well 

 exposed at the Hog's Back, where the following section was 

 measured. 



Ft. In. Ft. In. 

 7. Dark brown and black shale with ost- 



racods 4 4 



6. Rather pure, dark gray limestone with 



ostracods and bryozoa 1 5 



