SALT LAKE OOLITES 753 



He concluded that these oolites were of algal origin, and that the 

 oolites were built up within the membrane of the algal mass by the ac- 

 tivity of the algae, for he says : "The oolites of the Great Salt Lake are, 

 therefore, indubitably the product of lime-secreting fission-algae, and 

 their formation is proceeding day by day." ^^ Sherzer has several times 

 referred to these oolites and published very fine photographs of the com- 

 plete grains^^ (see figure 3, plate 26). Eothpletz failed to find nuclei 

 of foreign material in the oolites he studied, but their absence is not 

 characteristic of all of the oolites forming around the lake, as is clearly 

 shown in the descriptions of sections of these oolites about to be given. 



When tested by Meigen's reaction,^^ the oolites of the Great Salt Lake, 

 and also those from Pyramid Lake, Nevada, are found to be composed 

 of calcium carbonate in the mineral form aragonite, and hence agree 

 with those forming at Carlsbad and in the open ocean. In the thin sec- 

 tion on which the following description is based many of the oolites had 

 nuclei of foreign material, generally fragments of minerals, sharp and 

 angular in outline. The majority of these nuclei were clear and glassy, 

 except for minute inclusions. On examination with polarized light and 

 crossed nicols the majority of the grains proved to be sanidine, although 

 a few were plagioclase feldspar, showing numerous twin lamellae. A few 

 oolites were seen with nuclei of brown hornblende. The majority of the 

 oolites are spherical, although some are oval in section, and some are 

 even oblong, as if they were lengthwise sections of original cylindrical 

 grains with a length three or four times the shorter diameter. 



Micromeasurements of these oolites agree very closely with the meas- 

 urements given by Eothpletz and Sherzer. The large oolite shown in 

 figure 2, plate 26, is .58 mm. in diameter, although the great majority 

 of the spherical oolites are between one-third and one-half millimeter in 

 diameter. The nucleus of the large grain shown in the figure is .13 mm. 

 in diameter, while the nucleus of the adjacent smaller grain is .17 mm. 

 The largest observed oblong grain was .75 mm. in length by .25 mm. in 

 width. In a few of the more irregular grains the nuclei occupy over 

 one-half the diameter of the oolite. In one individual the nucleus was 

 a long angular fragment of sanidine, with a length of .43 mm. and a 

 width of .16 mm. The entire oolite surrounding this nucleus was only 

 a little over half a millimeter in length and about one-third a millimeter 

 in width. 



i»Loc. cit, p. 280. 



ao Michigan Geol. and Biol. Surv., Pub. 2, Geo!. Ser. 1, p. 37, pi. I, fig. B. Bull. Geol. 

 Soc. Am., vol. 21, pi. 46, fig. 4. 



21 W. Meigen : Centralb. f. Min., Geol., u. Pal., 1901, pp. 577-578. 



