REPORT OF TEE CEIEF ASTRONOMER 669 



SESSIONAL PAPER No. 25a 



are present in large amount. The shrinkage consequent on the loss of water of 

 crystallization amply accounts for the cavernous structure often seen in dolo- 

 mites. 



In conclusion, it appears that the hypothesis here proposed bears its third 

 principal test so far as the carbonates of calcium and magnesium are concerned. 

 It involves the precipitation of both carbonates from sea water through the decay 

 of animal matter. The magnesium carbonate should have been most abundantly 

 thrown down in pre-Cambrian time; its precipitation must have been lessened 

 through Paleozoic and Mesozoic time, and has reached its minimum since the 

 abysses of the ocean became abundantly tenanted with scavengers. 



Origin of Certain Iron Ores, Cherts, and Jaspers. — In the preliminary paper 

 a brief statement was given as to the possible origin of the lake Superior iron 

 ores, cherts, and jaspers through precipitation from sea water by ammonium 

 carbonate derived from decaying animal matter (American Journal of Science, 

 Feb., 1907, pp. 110-111). These subjects are not directly relevant in the present 

 connection and their discussion will not be attempted. Nevertheless, it may 

 be noted that the regular association of dolomite with the ores, jaspers, etc., 

 tends to corroborate the proposed hypothesis for the dolomites. 



Origin of the Petroleum and Natural Gas Emanating from Pre-Cambrian 

 Sediments. — Finally, the hypothesis of an almost limeless sea during Eozoic 

 times correlates well with the undoubted fact that natural gas and petroleum 

 are to-day issuing from pre-Cambrian strata. An excellent example of this 

 is seen in the field now being prospected in the Flathead valley of British Col- 

 umbia, at points situated far inside the eastern limit of the Rocky Mountains. 

 The entombment of the carcasses of soft-bodied animals is, it is true, partly 

 prevented by their bacterial decomposition, but doubtless not more so than by 

 the steady removal of carcasses from the sea bottom by scavengers. Murray has 

 shown that there is, in the deep-sea deposits of the present time, a considerable 

 percentage of organic (soft-bodied) matter. This fact is all the more striking 

 since there is evidence that the bottom muds are being worked over and over by 

 scavengers through whose bodies pass inorganic and organic matter together. 

 Before the general scavenging system for the sea floor was introduced we 

 should expect a still higher proportion of such organic matter to enter into 

 the composition of marine sediments. It is therefore not a matter of surprise 

 that sufficient organic (soft-bodied) matter was entrapped within Eozoic sedi- 

 ment to furnish, after subsequent distillation, the oil and gas actually seen 

 issuing from these old rocks. The greatest amount of entombment would be 

 expected after the marine animals had begun to cover themselves with shells 

 and skeletons (these structures retarding complete bacterial decay), and before 

 the scavenging system was well established; it may be partly for this reason 

 that the older Paleozoic formations are relatively so rich in petroleum and 

 natural gas. Nevertheless, these fluids may emanate from rocks in which there 

 is not a trace of shell or skeleton — rocks as unfossiliferous as so many pre- 

 Cambrian formations. 



