744 L. D. BURLING CAMBRO-ORDOVICIAN NEAR MOUNT ROBSON 



well. The very base of the overlying "Hota" contains typical Middle 

 Cambrian fossils, and the underlying "Tah" is abundantly fossiliferons, 

 all of the horizons discovered in the. latter being Lower Cambrian. 



(§ 31c.) The Mahto sandstones therefore represent an apparently 

 unfossiliferous qnartzitic series between the Middle Cambrian and the 

 first OleneUv^/^ and the line between the Lower and the Middle Cam- 

 brian is drawn at the top of the Mahto formation (§§ 8, 30e, 30/). 



(§ Sid.) Our estimated thickness of 1,200 feet for the Mahto in 

 Mumm Peak differs from Walcott's estimate of 1,800 feet for its thick- 

 ness in Mount Mahto, five miles away. The relation of the arenaceous 

 beds above to the calcareous beds below, which is the basis on which the 

 line is drawn in Mumm Peak, may vary in the distance separating the 

 latter peak from Mount Mahto. 



MURAL C'TAH") LIMESTONE FORMATION (§32) 



Mahto formation, as the name for the beds carrying the "new Lower Cam- 

 brian subfauna" : Walcott, Smithsonian Miscellaneous Collections, volume 

 57, number 11, 1913, pages 311-316. (According to Walcott, § S2(], this use 

 of the term Mahto was by error.) 



Hota formation, as the name for the beds carrying this fauna : Walcott, idem, 

 number 12, 1913, page 3.39. (An error in identification, § 32c.) 



Tah formation, as the unfossiliferous formation between the Mahto and the 

 McNaughton : Walcott, idem, pages 335 and 339. 



Tah formation : Burling, Museum Bulletin number 2, Geological Survey of 

 Canada, 1914, page 109. (On page 108 the reference of the "new Lower 

 Cambrian subfauna" to the Hota is questioned.) 



Tah formation : Walcott, Problems of American geology, 1915, page 179. 



Mahto formation : Walcott, Annual Report of the Smithsonian Institution for 

 1915, plate 17, 1916, page 254. (A reversion by inadvertence to the no- 

 menclature of the first reference, § S2d. ) 



Mahto formation, as the formation carrying one of the new Lower Cambrian 

 subfauna forms {Padeumias) : Burling, Bulletin of the Geological So- 

 ciety of America, volume 27, 1916, pages 158-159. (The error of placing 

 this fauna in the overlying "Hota" had been recognized, but the line be- 

 tween the Mahto and the underlying "Tah" was at this time drawn so as 

 to include the fauna in the Mahto— §§31&, S2d, 32e.) 



Mahto formation, as the formation carrying the Padeumias above mentioned : 

 Burling, Ottawa Naturalist, volume 30, 1916, page 55. (See note to pre- 

 ceding reference.) 



(§32a.) The "Talr' formation is described by Walcott as occurring 

 just above Moose Pass, at the base of "Tah Mountain," with a thickness 



25 It is, of course, possible tlmt the Olencllus fragmeuts credited to tlie Malito on page 

 335 of Walcott's paper did come from the Mahto, and that the formation is not unfos- 

 siliferous, as stated on page 369, and the rocks are so frequently fossiliferous that many 

 may be found in the Mahto by the next observer. 



