with which we have to deal.  The astronomer can employ material illustrations to give form and substance to our conceptions of celestial space; but such a resource is unavailable to the geologist.  The few thousand years of which we have historical evidence sink into absolute insignificance beside the unnumbered aeons which unroll themselves one by one as we penetrate the dim recesses of the past, and decipher with feeble vision the ponderous volumes in which the record of the earth is written.  Vainly does the strained intellect seek to overtake an ever-receding commencement, and toil to gain some adequate grasp of an apparently endless succession.  A beginning there must have been, though we can never hope to fix its point.  Even speculation droops her wings in the attenuated atmosphere of a past so remote, and the light of imagination is quenched in the darkness of a history so ancient.  In time, as in space, the confines of the universe must ever remain concealed from us, and of the end we know no more than of the beginning.  Inconceivable as is to us the lapse of “geological time,” it is no more than “a mere moment of the past, a mere infinitesimal portion of eternity.”  Well may “the human heart, that weeps and trembles,” say, with Richter’s pilgrim through celestial space, “I will go no farther; for the spirit of man acheth with this infinity.  Insufferable is the glory of God.  Let me lie down in the grave, and hide me from the persecution of the Infinite, for end, I see, there is none.”

CHAPTER I.

THE SCOPE AND MATERIALS OF PALAEONTOLOGY.

The study of the rock-masses which constitute the crust of the earth, if carried out in the methodical and scientific manner of the geologist, at once brings us, as has been before remarked, in contact with the remains or traces of living beings which formerly dwelt upon the globe.  Such remains are found, in greater or less abundance, in the great majority of rocks; and they are not only of great interest in themselves, but they have proved of the greatest importance as throwing light upon various difficult problems in geology, in natural history, in botany, and in philosophy.  Their study constitutes the science of palaeontology; and though it is possible to proceed to a certain length in geology and zoology without much palaeontological knowledge, it is hardly possible to attain to a satisfactory general acquaintance with either of these subjects without having mastered the leading facts of the first.  Similarly, it is not possible to study palaeontology without some acquaintance with both geology and natural history.