Lesley | 



118 



[Oct. L8, 



Without discussing in detail, at present, this instructive table, several 

 things are evident at a glance, viz : that 



1. Alternate strata of limestone and dolomite make up the mass. 



2. The dolomite layers carry the most insoluble materials, as a rule. 



3. Specimens taken from the top and bottom of the cut (thirty feet apart, 

 or less) differ sometimes as notably from one another as specimens taken 

 from different beds but, as a rule, each layer is nearly homogenous, so far 

 as two or three analyses can show such a rule. 



4. Not one of the so-called dolomite layers has enough carbonate of 

 magnesia to make it a true lithological dolomite. They are all merely 

 more or less magnesian limestones. 



5. Carbonate of magnesia is not absent from any bed in the whole 

 series ; but in an extensive range (such as from No. 84 to No. 115), out of 

 thirty-two beds twelve show less than two per cent., three show less than 

 three per cent., and one goes up to four and six-tenths per cent. The re- 

 maining sixteen beds, alternating with other sixteen with great regularity, 

 carry from thirty-six to fourteen per cent., nine of them ranging between 

 thirty six and thirty, five between thirty and twenty-five, one sinking to 

 seventeen, and one to fourteen per cent. 



The alternation in these thirty- two beds may be represented to the eye 

 thus : 



Per cent. 

 of Carb. Mag. 



Nos. of Beds selected from the Series. 



35 

 30 

 25 

 20 

 15 

 10 

 5 

 



and over. 



99 



