46 



Evolution and Distribution of Fishes 



S.'fl 



«£ 



c 



CO 



X 

 » ... 

 3lN 



2.S 



Silica 



Titanic acid 



Alumina 



Ferric oxide 1 . 

 Ferrous oxide j . 

 Manganous oxide 



Lime 



Magnesia 



Soda 



Potash 



68.12 

 o.i8 



15.81 

 5.01 



3.78 

 1. 18 

 5.09 

 1.06 



58.29 

 27.19 



8.27 



5.82 

 1.22 



52.3 



6.1 



27.7 



trace 



2.2 



13.6 



48.6 



8.2 



14.0 



18.9 

 11.6 



6.7 

 56.0 



99-23 



100.79 



101.9 



101.3 



In connection with such results Judd refers to the vary- 

 ing composition of the dust at different distances from the 

 centre of ejection and says that samples were taken "from 

 many points, ranging from 40 to 1,100 English miles away 

 from the volcano." Those nearest the volcano showed 

 "greater abundance in them of fragments of crystals, es- 

 pecially those of magnetite and other dark colored minerals. 

 Those dusts which were collected at the greatest distance 

 from the volcano were excessively fine and almost perfectly 

 white in color." 



The above exactly explains the varying aspect, composi- 

 tion, and consistency of many rock-strata occurring in all 

 formations from the Silurian upward, and which are usually 

 rich in the most finely preserved fossil remains. Judd's 

 conclusions are as follows: "Of the immense mass of com- 

 minuted matter thrown into the air 9/10 of this material 

 consisted of glass having a specific gravity of less than 2.3, 

 drawn out into fine threads and thin plates, often hollow 

 and containing bubbles of air, and sometimes in all prob- 

 ability reduced to particles of ultra-microscopic dimensions. 

 These particles of glass would tend to float by the adhesion 

 between them and air, and in the higher and rarer portion 

 of the atmosphere their suspension may not improbably 



