Heusser and Clarez suppose this decomposition of the rocks to be due to nitric acid.  But where did the nitric acid come from?

In short, here is the proof of the presence on the earth, just before the Drift struck it, of that conflagration which we shall find described in so many legends.

[1.  “The Geology of Brazil,” p. 25.]

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And certainly the presence of ice could not decompose rocks a hundred feet deep, and change their chemical constitution.  Nothing but heat could do it.

But we have seen that the comet is self-luminous—­that is, it is in process of combustion; it emits great gushes and spouts of luminous gases; its nucleus is enveloped in a cloak of gases.  What effect would these gases have upon our atmosphere?

First, they would be destructive to animal life.  But it does not follow that they would cover the whole earth.  If they did, all life must have ceased.  They may have fallen in places here and there, in great sheets or patches, and have caused, until they burned themselves out, the conflagrations which the traditions tell us accompanied the great disaster.

Secondly, by adding increased proportions to some of the elements of our atmosphere they may have helped to produce the marked difference between the pre-glacial and our present climate.

What did these gases consist of?

Here that great discovery, the spectroscope, comes to our aid.  By it we are able to tell the elements that are being consumed in remote stars; by it we have learned that comets are in part self-luminous, and in part shine by the reflected light of the sun; by it we are even able to identify the very gases that are in a state of combustion in comets.

In Schellen’s great work[1] I find a cut (see next page) comparing the spectra of carbon with the light emitted by two comets observed in 1868—­Winnecke’s comet and Brorsen’s comet.

Here we see that the self-luminous parts of these comets

[1.  “Spectrum Analysis,” p. 396.]

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burned with substantially the same spectrum as that emitted by burning carbon.  The inference is irresistible that these comets were wrapped in great masses of carbon in a state of combustion.  This is the conclusion reached by Dr. Schellen.

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SOLAR SPECTRUM

Padre Secchi, the great Roman astronomer, examined Dr. Winnecke’s comet on the 21st of June, 1868, and concluded that the light from the self-luminous part was produced by carbureted hydrogen.

We shall see that the legends of the different races speak of the poison that accompanied the comet, and by which great multitudes were slain; the very waters that

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first flowed through the Drift, we are told, were poisonous.  We have but to remember that carbureted hydrogen is the deadly fire-damp of the miners to realize what effect great gusts of it must have had on animal life.