Correspondence — Mr. 0. Fisher. 



379 



following the approximate rule. It will be seen that for angles less 

 than 15° this error is always less than one degree. 



r 



(1) 



(2) 



(3) 



(4) 



1 in 



1 in 



58' 



2' 



57-29 



60 



2" 



28-64 



30 



1° 55' 



5' 



3° 



19-08 



20 



2° 52' 



8' 



4° 



14-30 



15 



3° 49' 



11' 



5° 



11-43 



12 



4° 46' 



18' 



10° 



5-67 



6 



9° 27' 



33' 



15° 



: 3-73 



4 



14" 2' 



58' 



20° 



2-75 



3 



18' 26' 



1° 34' 



25° 



2-14 



2-4 



22° 37' 



2° 23' 



30° 



1-73 



2 



26° 33' 



3° 27' 



35° 



1-43 









40° 



1-19 









45° 



1 









Explanation. — 3° is actually 1 in 19-08 ; the approximate rule 

 gives it 1 in 20 ; 1 in 20 is 2° 52' ; error from following approx- 

 imate rule 8'. 



In Fig. 1 the dip along A B is 4° or 1 in 14-30, the dip along A C 

 is 15° or 1 in 3-73: ^^=1430, J. (7=373, dropping the decimals. 

 ^D is found to be 290. Hence the full dip is 1 in 2-9 or 19° very 

 nearly. A. H. Gkeen. 



Leeds, July 13, 1876. 



MR. MILNE ON FLOATING ICE, 



Sir, — When comparing the altitude of an iceberg above water 

 with the depth immersed, Mr. Milne has not sufficiently considered 

 the conditions of stable equilibrum. A berg of the shape figured on 

 page 307 could not remain in that position, but must turn over. 

 That this would be the case may be seen by placing a boxwood 

 tetrahedron (out of a set of models of crystals) in water, where it 

 will float only with one of its angles downwards. 



The position of stable equilibrium depends on the shape of the 

 floating body, and on its specific gravity. The specific gravity of 

 boxwood being about 0-95, is so nearly the same as that of ice, that 

 the positions assumed by a floating mass of either substance will as a 

 rule be almost identical. 0. Fisher. 



THE OLDEST FOSSILIFEROFS EOCKS OF NORTHERN EUROPE. 



Sir, — The evidence brought forward by Prof. Linnarsson in the 

 June Number of the Geological Magazine, as being opposed to the 

 views advanced by me, has been already disposed of to a great extent 

 in the papers in which these views have been propounded.^ That 

 Prof. Linnarsson is unable to put forward stronger evidence in op- 

 position to these views, is clearly a powerful argument in my favour, 

 and I doubt whether he would have raised the objection at all had 



^ Quart. Journ. Geol. Soc. vol. xxxi. p. 552 seq. ; Geol. Mag. Dec. II. Vol. III. 

 Nos. IV. V. VI. J 



