36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 75 



a full appreciation of the development of the formation in the Brisco- 

 Stanford Range was obtained. It was found that the formation has a 

 maximum thickness of 3,800 feet (1,158.2 m.), and the same four 

 faunules that occurred in it to the north are also present. The extent 

 and character of the formation and of its contained fauna is presented 

 in a preliminary manner in the account of the Sinclair Canyon and 

 Stoddart-Dry Creek sections. 



The fine exposures of the formation in the Beaverfoot-Brisco- 

 Stanford Range are the result of faulting and subsequent erosion of 

 the blocks delimited by the faults. On the west side of the range 

 Mons limestones and shales occur west of a major fault that occurs 

 between the several areas of the Mons and the Silurian limestones 

 of the westward facing cliffs of the range. One of the most important 

 of these exposures is that between Stoddart and Dry Creek Canyons 

 (see p. 21). Another is the long, narrow area at Brisco and the out- 

 crops from south of Harrowgate to the Kicking Horse Canyon at 

 Golden. All of these outcrops undoubtedly represent remnants of 

 what was originally a continuous outcrop of Mons from Golden to 

 Canal Flats, and which probably now extend far to the westward 

 beneath the Pleistocene floor of the Columbia River Valley (" Rocky 

 Mountain Trench "). 



Other major faults occur within the range to the eastward that 

 have delimited long strips of Silurian limestones on the east of the 

 western strip of Mons, also a second north and south strip of the 

 Mons east of the Silurian that extends over 5,000 feet (1,524 m.) up 

 the Sinclair Canyon with a dip of 60° to 80° before it is cut off by 

 the great " Red Wall breccia " fault. Another strip of the Mons 

 occurs east of the Silurian of the " Red Wall breccia " that has an 

 exposure of nearly 6,000 feet (1,828.8 m.) along the canyon, with a 

 high dip (70 "" to 90° west). How much duplication of strata occurs 

 by faulting and folding in these great exposures of the Mons is not 

 definitely known. 



In all known sections the Mons is superjacent to a massive cliff- 

 forming limestone beneath which a strongly developed Upper Cam- 

 brian fauna occurs in thin-bedded and shaly limestones. The Mons 

 is succeeded by limestones containing a fauna of lower Ordovician 

 age, unless they are absent by nondeposition as is quite frequently the 

 case. The lower Mons (Briscoia) faunule is strongly related to that 

 of the Upper Cambrian, and the upper faunule has a large proportion 

 of genera of an Ordovician facies. The discussion of the Mons fauna 

 will be taken up after the study of the collections is further advanced 

 and critical comparisons can be made with the Upper Cambrian and 

 lower Ordovician faunas. 



