754 T. C. BROWN OOLITES AND OOLITIC TEXTURE 



The oolites are composed of radially arranged fibrous aragonite around 

 these nuclei and give the characteristic dark cross between crossed nicols. 

 Some of the individual oolites show a somewhat coarser fibrous structure 

 extending throughout the greater part of their diameter. Outside of 

 thi5 and separated from it and from one another by distinct lines come 

 one or two very narrow zones of much finer fibers, likewise radially ar- 

 ranged. Two such zones occur in the large oolite grain shown in the 

 figure. These zones have been broken away at one or two points during 

 the grinding of the section. 



If, as Eothpletz claims, these oolites are formed by the organic activity 

 of minute algse, how can this very marked difference in the physical 

 make-up of the oolite be explained ? If the chemical origin of the grains 

 be admitted, the changes in structure can very easily be explained by the 

 changes in the solutions producing them, as will be shown hereafter. 

 While studying the oolites from the Eed Sea, Rothpletz observed certain 

 tubular structures within the oolites which looked like vermiform, some- 

 times branching, canals. . These he explained as formed by threadlike 

 algae which were not concerned in the formation of the oolite, but which 

 became imprisoned in the oolite as it formed. Can not the presence of 

 dead and crumpled cells of certain minute algse within the oolites of 

 Great Salt Lake be best explained in the same way, namely, as cells 

 which had selected the oolite as a point of attachment cincr became im- 

 prisoned within it by the further accretion of aragonite by chemical pre- 

 cipitation ? 



It is well kno^vn that the waters of Great Salt Lake are concentrated 

 solutions which vary both seasonally and periodically through wide limits. 

 The sets of analyses collected by Clarke, from which the following are 

 quoted, show this variation very clearly : 



Analyses of various Waters 



C A F G H 



CI 41.04 55.29 55.25 55.11 53.72 



SO* 5.25 7.69 6.73 6.66 5.95 



CO^ 14.28 .21 



Na 33.84 30.59 34.65 32.97 32.81 



K 2.11 1.11 2.64 3.13 4.99 



Ca 25 1.20 .16 .17 .31 



Mg 2.28 3.73 .57 1.96 2.22 



( 3.30- ) 

 Salinity per cent 35 1 3 74 ^ 27.72 22.99 17.68 



C. Pyramid Lake, Nevada. Mean of lour concordant analyses by Clarke. 

 Bull. 491, U. S. Geological Survey, page 147. 



