Geological Society. 391 



that found by Professor Seidel for the light of the stars. By 

 employing the table thus deduced, and also reducing the heat- 

 determinations obtained on the various nights for change of dis- 

 tance of the sun, a more accurate phase-curve was deduced, 

 indicating a more rapid increase of the radiant heat on approaching 

 full moon than was given by the formula previously employed, but 

 still not so much as Professor Zollner's gives for the moon's light. 



By employing Laplace's formula for the extinction of light in 

 our atmosphere, the heat-effect in terms of the scale-readings was 

 deduced, and an approximation to the height of the atmosphere 

 attempted. 



Prom a series of simultaneous measurements of the moon's heat 

 and light at intervals during the partial eclipse of November 14, 

 1872, when clouds did not interfere, it was found that the heat 

 and light diminish nearly if not quite proportionally, the minimum 

 for both occurring at or very near the middle of the eclipse, when 

 they were reduced to about half what they were before and after 

 contact with the penumbra. 



GEOLOGICAL SOCIETY. 

 [Continued from p. 314.] 



November 20, 1872.— Prof. P. Martin Duncan, F.B.S., V.P., 

 in the Chair. 



The following communications were read : — 



1. " On the Geology of the Thunder-Bay and Shabendowan 

 Mining Districts on the North Shore of Lake Superior." By H. 

 Alleyne Nicholson, M.D., F.G.S., &c. 



The author described the general characters of Thunder Bay, 

 which is almost landlocked on the south-east by the bold promontory 

 of Thunder Cape and a series of islands which form a continuation 

 of this. The rocks immediately surrounding Thunder Bay belong 

 to the "Lower and Upper Copper-bearing series" of Canadian 

 geologists. The latter, consisting of sandstones, shales, limestones, 

 marls, and conglomerates, chiefly of a red or reddish colour, with 

 inters tratified traps, is regarded by the author as probably of Lower- 

 Silurian age, in accordance with the opinion of Sir Wm. Logan. 

 The " Lower Copper-bearing series " is also very varied in character ; 

 it is traversed by trap dykes, and contains several well-marked 

 interstratified traps. It is penetrated by two sets of mineral veins, 

 containing great abundance of silver. The majority of these run 

 along the strike of the beds in a general E.N.E. and W.S.W. .direc- 

 tion ; the remainder are transverse, running nearly N. and S. Of 

 the latter the most important is the " Silver-islet vein," which is 

 3 or 4 feet in width, and consists of quartz with native silver and 

 galena ; picked specimens of the stuff have assayed from .£1000 to 

 £2000 per ton. This vein has been worked for about two }^ears, 

 and has proved remarkably productive. Of the former series the 

 most important is the " Shuniah vein," which runs along at a dis- 



