PSEUDOBRECCIATION IN ORDOVICIAN LIMESTONES 403 
ness of the division is about 130 ft. Like the Lower Mottled, this 
limestone is highly fossiliferous, and is characterized by the presence 
of fossils of large dimensions: various orthoceratites, Maclurea 
manitobensis and Receptaculites owent are particularly abundant. 
The mottled character of the stone will be subsequently described 
in detail. The chief difference that has been noted between this 
and the Lower Mottled is that frequently the pale-colored areas 
of the Upper Mottled are chalky in character, and readily soil the 
fingers, a feature not observed in the Lower Mottled. (5) The 
Stony Mountain formation, a series of ochreous shales overlaid by 
massive dolomitized limestones, showing a maximum thickness for 
the whole series of r10 ft. The beds thin out northward. The 
shales at the base are highly fossiliferous, and probably represent 
the Utica shales of the Cincinnati group. The top beds of the 
Ordovician in Manitoba are overlaid, presumably conformably, 
by the thin-bedded, dolomited limestone of the Niagara formation, 
exposed at Stonewall and at the mouth of the Saskatchewan River. 
Further detailed work is required before an exact correlation 
of these beds with the Ordovician of Minnesota, Wisconsin, and 
Iowa can be given. Pending this, the following alternative corre- 
lation is submitted, the latter of which seems with the present 
evidence the more probable. 
Minnesota, Wisconsin, and Iowa Manitoba Minnesota, Wisconsin, and Iowa 
Maquoketa shale Stony Mountain form Maquoketa shale 
(190 ft.) 
pper Mottled lime-' Galena dolomite 
“ stone (130 ft.) 
Galena dolomite = )Cat Head limestone Green shales (Black River) 
2 (70 ft.) | 
= {Lower Mottled lime- Plattville limestone 
stone (70 ft.) 
Green shales (Black River) Winnipeg sandstone St. Peter sandstone 
(100 ft.) 
Plattville limestone 
St. Peter sandstone 
THE MOTTLING OF THE LIMESTONE 
The quarries at Tyndall furnish good exposures of the Upper 
Mottled limestone. The following description applies more particu- 
larly to what was formerly known as Garson’s quarry, now under 
