226 



INDUSIAL LIMESTONE, AUVERGNE. [Ch. XIV. 



Tig. 166. 



Bed of indusial limestone, inters trati fie d with freshwater marl, near Clermont (Kleinschrod). 



We may often observe in our ponds the Phryganea (or Caddis-fly), 

 in its caterpillar state, covered with small freshwater shells, which they 

 have the power of. fixing to the outside of their tubular cases, in order, 

 probably, to give them weight and strength. The individual figured in 

 the annexed cut, which belongs to a species very abundant in England, 

 has covered its case with shells of a small 

 Planorbis. In the same manner a large 

 species of caddis-worm which swarmed in the 

 Eocene lakes of Auvergne was accustomed 

 to attach to its dwelling the shells of a small 

 spiral univalve of the genus Paludina. A 

 Larva of recent Phryganea* l mn dred of these minute shells are some- 

 times seen arranged around one tube, part of the central cavity of which 

 is often empty, the rest being filled up with thin concentric layers of 

 travertin. The cases have been thrown together confusedly, and often 

 lie, as in fig. 168, at right angles one to the other. When we consider 



Fis. 168. 



a. Indusial limestone of Auvergne. 5. Fossil Paludina magnified. 

 ■* I believe that the British specimen here figured is P. rhombica, Linn. 



