334 PRINCIPLES OF STRATIGRAPHY 



exceeded by Tertiary and later formations if more analyses were 

 available. Daly points out that the ratio of calcium to magnesium 

 in all pre-Devonic formations is significantly close to the same 

 ratio in the rivers now draining pre-Cambric terranes, as shown by 

 the Ottawa River, where the average ratio is 3.69: i. From this 

 he suggests that during pre-Devonic time the river-borne magne- 

 sium and calcium were wholly precipitated, after diffusing, to the 

 sea bottom. Daly holds that the study of the grain of unmeta- 

 morphosed Cambric and pre-Cambric carbonate rocks convincingly 

 shows that they are not of clastic origin nor of -direct organic origin 

 through accumulation of shells or skeletons. Microscopic exami- 

 nations of typical specimens from a mass more than 7,000 feet 

 thick seem to indicate that neither horizon nor distance from the 

 old shore lines afifects the singularly monotonous grain of the 

 rocks. "The constituent particles are either idiomorphic and 

 roughly rhombohedral, or anhedral and faintly interlocking. The 

 former are everywhere of nearly uniform average diameter, rang- 

 ing from o.oi mm. to 0.03 mm., with an average of about 0.02 mm. 

 The anhedral grains range from 0.005 i^^""*- to 0.03 mm., averaging 

 about 0.015 "^"1- ^^"^ diameter.'' (Da.\y-i2: 168.) A similar uni- 

 formity of grain was found in the Archaean dolomites of Idaho, in 

 the magnesian limestones and dolomites of the Belt terrane with 

 Beltina danai, in the Clarke range, and in the Siyeh and Sheppard 

 siliceous limestones of northwestern Montana (Middle Cambric). 

 Similar fine-grained dolomites have been found by Vogt in Nor- 

 way, and are believed to be chemical precipitates. (Vogt-55, 

 quoted by Daly-12 : zd^".) An apparently good case of lime 

 deposition in the sea by chemical separation, through the influence 

 of decaying organic matter, is found in the fine calcareous and 

 magnesian mud at the bottom of the Bay of Naples. (Walther and 

 Schirlitz-67 :?j?d.) This mud is relatively poor in organic remains, 

 and seems to have been separated from the lower strata of water, 

 which are poorer in lime and magnesia than the upper. Stony 

 crusts consisting chiefly of calcium carbonate, of ferruginous clay, 

 of double silicates of sodium and potassium holding manganese, of 

 silica, and of carbonate of magnesia are found at the bottom of 

 several mediterraneans, as, for example, the Roman Mediterranean 

 between Crete and Africa on the one hand, and Crete and Asia 

 Minor on the other. Also between Crete and Greece and in parts 

 of the iligean Sea, as well as in the Red Sea, where they are com- 

 mon, and the bottom waters are rich in ammonia ( Phillipi-45 • 

 439.) Calcareous concretions were dredged by the CJialleiiger from 

 a blue clay in 216-255 ^^^- depth west of New Guinea, and these are 



