324 Canadian Record of Science. 



based on these estimates, but they at least show the possi- 

 bility of its being much higher than the 744 feet above 

 the level of the St. Lawrence, which is the present highest 

 point of the mountain. 



There is, however, corroborative evidence in the nature 

 of the trap of Mount Eoyal itself, and in this respect 

 the same rule is found to apply, to some extent at 

 least, to the other intrusive masses belonging to the 

 same seiies, namely, Yamaska, Eougemont, Beloeil, 

 Montarville and Eigaud. The structure of the mass 

 in all these cases is highly compact, and crystal- 

 line, which would indicate that they were ejected and 

 consolidated under great pressure. Some of them reach a 

 height of more than 1,000 feet above the plain, and their 

 summits appear equally solid and crystalline with their 

 bases. Eeasoning from these facts, it would appear that 

 the level of the Lower Silurian strata must in all proba- 

 bility have reached a point far above the present summit 

 of Mount Eoyal. 



If this assumption is correct, there would be at the 

 close of the period in which the Hudson Eiver formation, 

 including the Utica and Trenton, was laid down, a great 

 plain, with few inequalities, and covered with solid rock^ 

 extending from the Lauren tian to the Adirondack 

 Mountains. 



An interesting question arises here as to the date or 

 distance of time when the eruption took place. Any esti- 

 mate which may be made of this date must of necessity 

 be largely a mere deduction from certain supposed prem- 

 ises, both of which may be altogether mistaken. Various 

 attempts, however, for the most part widely divergent, 

 have been made to fix the date, some of which have been 

 placed at over 100,000,000 years. Among others, Lord 

 Kelvin, better known as Sir William Thomson, whose 

 opinion is perhaps of as much value as that of any one, 

 has estimated the whole duration of the earth at 20,000,000 

 years. 



