JS. O. Hovey — Cherts of Missouri. 405 



this interesting rock : Wright County, Camden County, Mor- 

 gan County, Osage River, and Taney County, in Missouri. Mr. 

 Winslow reports that the oolitic chert of the Missouri Lower 

 Magnesian strata is of common occurrence and that frequently 

 the beds are more than a foot thick. One of the Lower Mag- 

 nesian localities furnishes a rock which is partly oolitic in struct- 

 ure and two others give rocks in which rounded grains of quartz 

 have been cemented in an abundant matrix of chalcedony, 

 without the formation of concretionary spherules about them. 

 In one of the latter, however, the chalcedony shows that there 

 was some tendency within it to form shells about the quartz 

 grains, and an occasional small spherule of chalcedony may be 

 seen in the matrix. 



Chemistry. — As was to be expected from the microscopic 

 characteristics, the cherts, when not fossiliferous, are almost 

 pure silica. The analyses made by the Missouri Geological 

 Survey show a much higher percentage of alumina and iron- 

 oxide than is present in the cherts from the same strata and 

 the same general region which were analyzed by the IT. S. 

 Geological Survey, but this difference is probably due to the 

 fact that the specimens analyzed by the Missouri survey were 

 selected more to illustrate the transitions between cherts and 

 other rocks than to exemplify pure chert. Mr. Robertson 

 reports that in making the analyses the Al 2 3 + Fe,0 3 was 

 redissoWed after the first precipitation and precipitated again 

 to make sure that no Si0 3 was included in the amount. The 

 percentage of soluble silica was determined in only four of 

 these analyses : Prof. Seamon, in his report on No. 11 for the 

 Tripoli company, says that " 7'28 per cent of the silica was 

 soluble in a 10 per cent solution of caustic soda on boiling for 

 three hours ;" the U. S. Survey reported 4/52 per cent in No. 

 13, 3-99 per cent in No. 14 and 3 35 per cent in No. 18, and 

 that the determination was made in the following manner : 

 the solution used was made up of one part solid caustic potash 

 to three parts water, and one gram of the finely powdered 

 chert was heated in each case with fifty cubic centimeters of 

 the solution for one hour on the water bath. No. 14 was 

 somewhat porous, Nos. 13 and 18 were compact, the last 

 showing occasional cavities filled with quartz crystals.* These 

 percentages, however, cannot be taken as the measure of the 

 amorphous silica present in these rocks, for undoubted quartz 

 is noticeably soluble in caustic potash, Rammelsbergf finding 

 from 5 to 7*75 per cent of vitreous massive quartz thus soluble, 

 and quartz crystals and quartzite tested for the Arkansas Sur- 

 vey:}: gave from 2 # 59 to 6*28 per cent soluble in this medium. 



* Ark. Geol. Surv., Ann. Rep., 1890, vol. in, Novaculites, p. 161. 

 f Quoted in Dana's Syst. Mineralogy, 5th ed., p. 193. 

 t'Op. cit, p. 164. 



