PILOT AND STAR MOUNDS. 99 



very abundant easts of Inoceramus ])i'ohlematicus Schlot. Scales of fishes 

 are also found in both the limestone and sh^le.' 



The Tiger Hills, extending westward from the north end of the Pem- 

 bina Mountain, consist of the Fort Pierre shales, eroded in massive rounded 

 elevations and overlain by drift from a few feet to 50 feet or more in thick- 

 ness, much of which has the rough contour and abundant bowlders char- 

 actei'istic of terminal moraines. Thence southward to the international 

 boundary the shale is frequently encountered at moderate depths in digging 

 wells ; and here and there remnants of its highest beds form isolated liills, 

 which show that much erosion has taken place during a former baselevel- 

 ing of the surroimding plain country. Pilot Mound, in section 20, town- 

 ship 3, range 11, about a tliird of a mile in diameter at its base and rising 

 steeply 80 feet above the general level to a rounded siTmmit about 1,630 

 feet above the sea, thus consists of the hard upper portion of this shale 

 formation, thinly covered with drift. Star Mound, a more massive and 

 moderately sloping elevation, situated in sections 22, 23, 26, and 27, town- 

 ship 1, range 10, about 15 miles southeast of Pilot Mound, is of the same 

 character. The base of this hill extends three-fourths of a mile from east 

 to west and a third of a mile or more from north to south ; and it rises 

 with a very regular oval form to a small ])lain 30 to 40 rods long from 

 east to west and half as wide at its top, which is 100 feet above the adjoin- 

 ing country and about 1,650 feet above sea-level. 



At the Nioljrara outcrop on the Assiniboine the base of the Fort Pierre 

 formation is about 950 feet above the sea ; on the Vermillion River it is 

 stated by Tyrrell to be at 1,205 feet ; and on the Swan River it is probably 

 not higher than 1,200 or 1,300 feet. Above these elevations the Fort PieiTe 

 shales form the upper portion of Riding- and Duck mountains and of the 

 Porcupine and Pasquia hills, reaching to the depth of several hundi'ed feet 

 beneath the glacial drift along the entire course of this great escarpment. 



The records of common and artesian wells in Chapter X contain 

 further notes of the Cretaceous formations underlying" the drift on the Red 



>My thanks are due to Mr. J. F. Whiteaves, of the Canadian Geological Survey, for his kind 

 assistance in the identification of these fossi Is. A series of the variable small Ostrea obtained at this 

 locality, and from the same formation on the Boyne and in the district of the Riding and Duck moun- 

 tains and northward, was submitted by him to Dr. C. A. White, who refers them to 0. congesta Conrad. 



