REPORT OF TEE CHIEF ASTRONOMER 



665 



SESSIONAL PAPER No. 25a 



brian and Cambrian limestones averaged is, in both cases, low, but includes 

 nearly all that seemed to be available. The number of the Tertiary and later 

 limestones averaged is again low, but the labour of searching for additional 

 ones did not seem necessary, since it is well known that these later limestones 

 are usually very low in magnesium. Lesley had already prepared a remarkable 

 series of analyses (230) which was intended to afford the average ratio for the 

 Ordovician limestones of Pennsylvania. This result could not, however, be 

 safely used, inasmuch as the whole series refers only to some 370 feet of beds 

 out of several thousand feet of the limestones locally developed, and at that 

 represents only a local phase of the Ordovician.f It has thus seemed better to 

 use the analyses derived from many Ordovician formations in Canada and the 

 United States. The ratio for the pre-Cambrian may be a little too high, for 

 the reason that thirty-three out of the sixty-one analyses selected were taken 

 from Miller's Bureau of Mines report on the limestones of Ontario, in which 

 there was some tendency to select limestones specially adapted to lime burning. 

 Excluding twelve analyses of specimens from limekiln quarries in Ontario, the 

 average ratio for the remaining pre-Cambrian rocks is 3.61 : 1. 



The results of the compilation and calculation are given in Table XLIII :— 



Table XLIII. — Calcium and magnesium in limestones of the geological periods. 



Period. 



Pre-Cainbrian. 



a. From N. America except those in b 



b. From Ontario ( Miller) 



c. Average of a and b 



Cambrian (including 17 of the Shenandoah limestone). 



Ordovician 



Silurian 



All pre-Devoniau 



Devonian . . 



Carboniferous 



Cretaceous 



Tertiary 



Quaternary and Recent 



Total, 865. 



Number 

 of analyses 

 averaged. 



28 



33 



61 



30 



93 



208 



392 



106 



238 



77 



26 



26 



Ratio 

 of CaC0 3 

 to MgCOs. 



1.64 

 4.92 

 2.93 

 2.96 



2.72 



2.09 



2.39 



4.49 



8.89 



40.23 



37.92 



25.00 



Ratio 



of 



Ca to Mg. 



2.30 : 1 

 6.89 : 1 

 4.10 : 1 

 4.14 : 1 



3.81 : 1 



2.93 : 1 



3.55 : 1 



6.29 : 1 



12.45 : 1 



56.32 : 1 



53.09 : 1 



35.00 : 1 



t J. P. Lesley: Final Report of Pennsylvania Survey, Vol. 1, 1892, p. 327. 



