been made in astronomy by the help of the telescope, and lately by that of the spectrum analysis,' we must still say with Burmeister, "The discoveries that have been made as to the nature of the separate heavenly bodies are unimportant; and as our power of observation is defective, being only possible at too great distances with insufficient means, it is hardly calculated to enlighten us in full even as to the physical condition of those bodies, much less can it give us a definite idea of their history, the stages of their development, or their inhabitants. As regards the earth, we have certainly-thanks to the untiring and careful examination of the strata which lie under the surface-obtained a mass of most important information; but it is both in a high degree possible and very desirable that this should be completed." Huxley says, "Water covers three-fifths of the whole surface of the globe, and has covered it in the same manner ever since man has kept any record of his own observations, to say nothing of the minute period during which he has cultivated geological inquiry. So that three-fifths of the surface of the earth is shut out from us, because it is under the sea. Let us look at the other two-fifths, and see what are the countries in which anything that may be termed searching geological inquiry has been carried out, a good deal of France, Germany, Great Britain. and Ireland, bits of Spain, of Italy, and of Russia have been examined; but of the whole great mass of Africa, except parts of the southern extremity, we

1 Cf. Natur und Off. 1868, p. 154. Pfaff, Die neuesten Forschungen, etc.,

2 Geschichte der Schöpfung, p. 1.

1

know next to nothing; little bits of India, but of the greater part of the Asiatic continent, nothing; bits of the Northern American States and of Canada, but of the greater part of the continent of North America, and in still larger proportion, South America, nothing. Under these circumstances, it follows that even with reference to that kind of imperfect information which we can possess, it is only about the ten-thousandth part of the accessible parts of the earth that have been examined properly." The greatest depth to which the earth has been penetrated is about 4000 feet, not quite twotenths of a geographical mile,2 about the 4700th part therefore of the diameter of the earth. According to a striking saying of Nöggerath's, the deepest mines and borings are only as the stings of a gnat in comparison to the diameter of the earth. If you imagine the earth to be represented by a globe 16 inches in diameter, the thickness of the paper which is pasted over it will represent the portion of the earth's crust which has as yet been examined. The scratch made by a needle on the varnish of the globe is comparatively as deep as the deepest mine. Lyell estimates the extent of the ground which has been examined, and from which we may draw conclusions, to be about the 400th part of

1 Huxley, On our Knowledge of the Causes of the Phenomena of Organic Nature, p. 37. Hæckel, Nat. Schöpfungsgesch., p. 345, "If, according to Sir John Herschel's latest calculations, the proportion of land to sea is as 57:146, the proportion of that which has been geognostically investigated is at most 12:51. More than half of the twelfth part of the earth has been cursorily observed by one or two men of science. Detailed investigations, such as are described in English, German, and French books, exist at most in a twelfth part of the twelfth part." Fraas, Vor der Sündfluth, p. 42.

2 Pfaff, Schöpfungsgeschichte, 2nd ed. p. 213. 3 Ges. Naturwiss., iii. 138.

the earth from the surface to the centre.1 "All that lies under this," says Humboldt, .. is even as

much unknown to us as is the interior of other planets belonging to our system. Where all knowledge

of the chemical and mineralogical natural constitution of the interior of the earth fails us," he adds, "we are again thrown upon conjecture, just as we are with reference to the farthest bodies which revolve round the sun." "Who shall guarantee us," he says in another place, "that the entire number of the vital forces efficient in the universe has been fathomed?" 2

The book of nature then is still in great measure closed to man, and although many leaves now lie open before us, which were unread half a century ago, no one will deny that there is still much which we cannot understand; and that although the progress of inquiry may give us data which are now unknown to us, much will probably always remain unfathomed by us on earth; natural science in this age cannot even claim to know its own province thoroughly, and an absolute completeness of observation must, humanly speaking, remain for ever an unattainable ideal. "The sciences of experiment," says Humboldt, "are never complete; the realm of the impressions of sense is not to be exhausted; no generation of men will ever have it in their power to boast that they have surveyed the whole of the world of phenomena." "

But the branch of natural science with which we shall be principally concerned, geology, does not con

1 Elements of Geology, i. 2.

2 Kosmos, i. 166, 167, 31; Eng. tr. 170, 33.

3 Kosmos, i. 65; Eng. tr. 67.

fine itself to the scientific examination of the earth in

its present condition. It endeavours by help of the knowledge of its present condition, and of the forces and laws of nature now at work, to ascertain what were its earlier stages, and to discover what changes have taken place since the beginning. Science has undoubtedly made surprising advances in this direction also in this century. The theories which were formerly propounded in the name of geology, or geogony, were in many cases only arbitrary speculations and pictures of the imagination, which could have no claim to scientific truth, because it was unhesitatingly assumed that forces and laws had been at work of whose existence

there is no proof. But this has now been entirely given up. Burmeister says, "We must explain the

signs of past change entirely from the condition in which we find the earth at the present time. For all scientific experience proves that the same forces are still at work in the earth which have developed and altered its surface since it first existed in space as a distinct body. A close study of its present condition must therefore be the foundation of all knowledge of its history, and armed with the results of these inquiries, we may endeavour to explain and represent the earlier periods." 1

1

Now if, as we have seen, our information concerning the present condition of the earth is so imperfect, it is impossible that geology, whose knowledge is entirely based upon this information, should fulfil its task. But further, in geology the question is not what are the facts, but what are the conclusions from these facts.

1 Geschichte der Schöpfung, p. 2.

"Those statements," continues Burmeister, "which we call hypotheses, must always play a great part in our history of creation: the further the time we are considering is from the present, and the less an event can be investigated and understood by the help of present facts, the more we must have recourse to hypotheses."

"1

Now no doubt many scientific hypotheses are based on facts which are so completely proved, and on conclusions which are so undeniable, that their probability borders on certainty, and they may therefore be the foundation of a scientific theory. But, on the other hand, there are many points in which such probability has up to this time not been attained, and in the course of our inquiries we shall find more than one case in which a hypothesis has been universally acknowledged as scientifically certain, and yet has been proved later to be erroneous. Finally, from the differences of opinion which prevail among the most eminent savants, we may infer that on many points of geology there are no certain conclusions.

"The most confident men of science," says Deutinger with truth, "will not deny that in natural science error is even now in many cases not only possible, but up to a certain point even inevitable." Really thorough inquirers are very modest in their estimate of what geology and natural science can declare to be perfectly assured results, and they are very strict in their criticism of hypotheses about the earlier periods of the earth's history. After Huxley has enumerated