Looking back into the past the nineteenth-century historian finds his sight speedily striking a mist and at last plunging into inky darkness. Bound down in fact by the influence of a ridiculous dogmatism which allows only some six thousand years for man's life on earth, he is unwilling to accept the old chronologies of the Egyptians or Hindûs, and, while permitting the assumption of vast periods for geological changes, he is staggered by a few millions of years more or less when they are added to the length of time during which humanity has peopled the globe. The student of Theosophy, however, sees no reason why he should doubt the statement made by his teachers on this subject. He knows that the periods of evolution are endless. These are called Manvantaras, because they are between two Manus, or, two men. These periods may be called waves whose succession has no cessation. Each grand period, including within it all the minor evolutions, covers 311,040,000,000,000 human years; under a single Manu the human years come and go, 306,720,000 in number, and the lesser yugas--or ages--more immediately concerning us, comprise of solar years 4,320,000. During these solar revolutions the human races sweep round and round this planet. Cave-dwellers, lake-dwellers and those of a neolithic or any other age appear and disappear over and over again, and in each of those we who now read, write and think of them were ourselves the very Egos whose past we are trying to trace. But, going deep into geological strata, the doubt of man's existence contemporaneously with the plesiosaurus arises because no fossil _genus homo_ is discovered in the same stratum. It is here that the theories of the Theosophist come in and furnish the key. Those hold that before man developed any physical body he clothed himself with an astral form; and this is why H. P. Blavatsky writes in her _Secret Doctrine_: "it teaches the birth of the _astral_ before the _physical_ body, the former being the model for the latter." At the time of the huge antediluvian animals they absorbed in their enormous bodies so much of the total quantity of gross matter available for frames of sentient beings that the astral man remained without a corporeal frame, as yet unclothed "with coats of skin." For this reason he could exist in the same place with those huge birds and reptiles without fear. Their massive proportions inspired him with no terror, and by their consumption of food there was no lessening of his sustenance. And, therefore, being of such a composition that he left no impression upon mud or plastic rock, the death of one astral body after another left no fossil and no mark to be unearthed by us in company with the very beasts and birds which were his contemporaries.