I02 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



the undecided questions is the stopping of growth at the top of each 

 layer of Hmestone. Why some of the stronger forms did not extend 

 above the level top surface of the layer in which they are found, it 

 is difficult to conjecture. It may be that a strong current swept away 

 the smaller pieces and filled in the interspaces among the larger forms. 

 It is planned to give attention during the field season of 1914 to the 

 occurrence of the large masses in the Newland limestone with 

 special reference to their mode of growth. 



Mineral composition. — A compact specimen of Camasia spongiosa 

 with very small opening into which the calcareous mud could pene- 

 trate gave the following result as determined by Dr. Edgar T, 

 Wherry of the United States National Museum: 



Oxides 



CaO 40.52 



MgO I. IS 



CO. + H2O 3338 



Fe.Oa + AUOs 372 



Si02 21.08 



99.85 



An analysis of a second specimen from which the calcareous 

 matter deposited within the cellular openings had been removed by 

 solution in hydrochloric acid gave the following: 



Oxides 



CaO 10.88 



MgO 0.27 



COo-fHaO 10.20 



FezOa + AUOs 10.22 



SiO. 68.32 



99.89 



The second analysis may be taken as indicating the present min- 

 eral composition of the deposit made by the algae. What its origi- 

 nal composition was cannot well be determined as there has evi- 

 dently been a large replacement by silica unless there was some 

 unrecognized siliceous sponge associated with it that furnished the 

 silicia. 



Microscopic structure. — Being fairly well convinced from the 

 comparison of " Lake Balls " and other recent massive calcareous 



