THK SUCCKSSION OF DEPOSITS. 43 



when, as is not infrcMiucnl, we luive two sets nearly at 

 riglit an.nles to each otlier, in the same locahty. Hence it 

 becomes an important; (juestion to ascertain the rehitive 

 ages of the slrialion, ami also the direction in which the 

 abradinu force moved. 



Takino' the valley of the St. Lawrence in the first 

 instance, the cra,u-and-tail forms of the isolated hills of 

 trap, like the Montreal monntain, with ahrupt escarp- 

 ments to the north-east and slopes of delais to the sonth- 

 west, the quantity of l)oulders carried from them far to 

 the south-west, and the prevailin.u striation in tiie same 

 direction, all jjoint to a gericral movement of detritus uj) 

 the St. Lawrence valley to the south-west. Further, in 

 some cases the striae themselves show the direction of the 

 ahradino- force. For example, in a iine exposure recently 

 made at the Mile-end (piarries, near :NL)ntreal, the polished 

 and trrooved surface of the limestone shows four sets of 

 striae. The principal ones have the direction of S. 68° W. 

 and S. 60" W. respectively, and the second of these sets 

 is the stronoer and coarser, and sometimes obliterates the 

 first. The two other sets are comparatively few and 

 feeble striae, one set running nearly N. and S., and the 

 other N.W. and S.Fl These last are probably newer than 

 the two first sets. Xow, with regard to the direction of 

 •the principal sets of striae, this at the locality in question 

 was rendered very manifest by the occuri-ence of certain 

 trap dykes crossing the limestone at right angles to the 

 striae. The force, whatever it was, had impinged on these 

 dykes from the N.E., and their S.W. side had protected 

 the softer limestone. The locality is to the X.E. of the 

 mass of trap constituting the Montreal mountain, and the 

 movement must have been up the St. Lawrence valley 

 from the N.E., and toward the mountain, but at this 



