. UNCONFORMITY AT BASE OF ONONDAGA LIMESTONE 311 
to be essentially the same in Ontario as it is in New York. The 
basal beds of the Onondaga are more or less sandy and approach 
in appearance the Oriskany sandstone below but contain no 
Oriskany fossils. The Oriskany sandstone is highly irregular 
both in thickness and in distribution in Ontario as it is in central 
New York. It is frequently absent from the sections showing the 
Onondaga limestone. Where it is present it may thin from a 
thickness of 15 ft. or more to a few inches in a distance of a few 
rods. This probably results in large part from the Oriskany sand- 
stone filling troughs of erosion in the Salina formation. The ac- 
companying diagram (Fig. 5) shows the relations of the Onondaga 
limestone and subjacent Oriskany and Salina formations near 
Decewsville, Ontario. An excavation about 200 ft. northeast of 
300’ 
Fic. 5.—Section exposed in vicinity of Oneida Sand Company’s quarry, Decews- 
ville, Ont.; A, Salina beds; B, Oriskany sandstone; C, Onondaga limestone. 
the Oneida Sand Company’s quarry two miles northwest of 
Decewsville shows the following section: 
DECEWSVILLE SECTION 
liramdagia IIMeSCOMGr es ae ai: esis a vino eins tee itis oe Otte 
inisermy SAMGStONe y. coil c.c.- = cura sipieysiewe cio tin diecisiae 3+ 2S = 2 £7 ine 
ikimestone.( Salina fOrmation)!. j2.4+- 26620. 0. a05 sees cae 30 ft. 
In the quarry less than 200 ft. from the above section the Oriskany 
sandstone has thickened to nearly 20 ft., as shown in the diagram. 
Where the Oriskany is absent the Onondaga-Salina contact is 
doubtless sometimes as irregular as the Oriskany-Salina contact 
shown in Fig. 5. But the limited number of good exposures 
and the absence of quarries where the Oriskany is wanting leave 
the character of the Onondaga-Salina contact to be inferred from 
the nature of the Oriskany-Salina disconformity. While the 
physical evidence of the disconformity at the base of the Oriskany 
