356 E. M. KINDLE 



the observation of Lieutenant Evans for six years, who reported 

 that there was an annual addition to them sometimes amounting 

 to half an inch in thickness which began to deposit in October 

 with the change in direction of the prevailing currents and which 

 was later in the year in part re-dissolved by the waves. ^ This 

 resolution of the calcium carbonate clearly indicates a seasonal 

 factor in the formations of some limestones, deposition proceeding 

 during only a portion of the year. 



Variability of the Molluscan contribution. — The relative abun- 

 dance of marine life on different parts of the sea bottom must be 

 an important factor in the variation in rate of limestone accumu- 

 lation in different areas. The general tendency of animal life to 

 flourish best in shallow water is a well established fact. "Very 

 many observations point to the conclusion that the density of 

 life, both fishes and invertebrates, is greater on the sea bottom in 

 close proximity to the land than in deeper waters farther out to 

 sea. It is in such inshore waters that one finds the greatest 

 wealth of animal life. "^ On the beach itself certain forms of 

 marine life flourish in extraordinary abundance. At Fleshmick on 

 the Isle of Man 2,940 individuals of Balanaus balanoides have 

 been counted on one square foot of sea shore.^ 



In fresh-water lakes molluscan life is practically limited to 

 depths less than 25 feet. Although a few fresh- water species 

 have a bathymetric range much greater than this the contribution 

 of such species to the calcareous element of lacustrine sediments is 

 almost negligible. The bathymetric limitations of marine faunas 

 are less abruptly drawn than those of fresh-water molluscan 

 faunas, but they tend in the same direction, viz., toward a decrease 

 in the amount of bottom life in deep water. It is evident from these 

 facts that the molluscan contribution to limestone sediments would 

 be largest along the inshore margin of the littoral zone. The sea- 

 ward decrease seems to be somewhat irregular. This contribution 



' Charles Darwin, Geol. Observations (1851), p. 49. 



^ James Johnson, Conditions of Life in the Sea. A Short Account of Quantitative 

 Marine Biological Research (1908), p. 176. 



3 Catherine Maynie, "Marine Biology at Port Erin," 52^ Ann. Rept. (1918), 

 p. 12. 



