Notices of Memoirs — Juhes-Broione — MonocUnal Flexures. 505 



Both specimens were discovered by John Jelly, Esq., of Shelburne. 

 The following measurements are given for comparison : — 



Longest rib 



Humerus 



liadius 



Femur 



Tibia 



Tusk 



Third spinnus process 

 The bones obtained of the Mammoth are not so numerous, the 

 chief being thirty-one ribs, one 50 inches in length and 11 in cir- 

 cumference ; several vertebrge, some 14^^ inches across ; a massive 

 tusk 12|- feet with a portion broken off; and a tooth weighing 

 16|- lbs. The writer also refers to remains of Proboscoidea found at 

 other points in Ontario, viz. St. Catherine's Dunville, Goat Island, 

 Niagara Falls, and Kimbal, near the western side of the Province. 



YIII. — The Cause of Monoclinal Flexure. By A. J. Jukes- 

 Browne, F.G.S. 

 FOLDS of the ordinary arch and trough type are generally ascribed 

 to the influence of lateral pressure ; but it is not easy to see 

 how a monoclinal flexure which appears in section as a flexui'e 

 connecting two horizontal bars of strata can have been produced by 

 direct lateral pi'essure exerted at the ends of the bars. 



The author suggests that monoclinal flexuring is a structure 

 impressed upon a horizontal series of uncompressed strata by the 

 displacement of a subjacent mass of faulted and flexured rocks, the 

 lateral compression of the deep-seated mass resulting in the vertical 

 uplift of certain portions of the ' cover.' If a series of stratified 

 rocks rests in a horizontal position on a mass of ancient rock, which 

 has been compressed, indurated, flexured, and faulted before the 

 deposition of the upper series, it is supposed that the lower series of 

 rocks would give way under lateral pressure along the pre-existing 

 faults, and that the blocks which lie between upward diverging 

 faults would be forced to move upwards, carrying with them those 

 tracts of the ' cover ' which rest on them. It is evident that these 

 tracts would be divided from those resting on blocks defined by 

 downward diverging faults by faults or monoclinal flexures, the 

 production of a fracture or a flexure depending partly on the thick- 

 ness and pliability of the strata forming the cover, and partly on 

 the amount of local uplift. It is conceivable that the displacement 

 might take place partly by faulting and partly by flexuring, and 

 that what was a fault near the plane of unconformity might pass 

 upward into a flexure. 



The writer desires criticism on the above suggestion, especially 

 from those who will have a chance of seeing the grand monoclinal 

 flexures of the Colorado region during the excursion of the approach- 

 ing International Geological Congress. 



1 The Newburg Mastodon is one of the finest ever discovered in America. The 

 bones are in a most excellent state of preservation, and sufficient have been obtained 

 to enable the skeleton to be set up. 



