191 



SCIENTIFIC SIDE-LIGHTS 



that cracks should have occurred in such a 

 position rather than in others was probably 

 owing to the greater motion at such a place, 

 due to the face of the cliff being unsup- 

 ported, and there being no resistance op- 

 posed to its forward motion. It often hap- 

 pens that earthquake cracks are many feet 

 in width. Ac the Calabrian earthquake of 

 1783, one or two of the crevasses which were 

 formed were more than 100 feet in width 

 and 200 feet in depth. Their lengths varied 

 from half a mile to a mile. Besides these 

 large cracks, many smaller ones of one or 

 two feet in breadth and of great length were 

 formed. In the large fissures many hous- 

 es were engulfed. Subsequent excavations 

 showed that by the closing of the fissures 

 these had been jammed together to form one 

 compact mass. MILNE Earthquakes, ch. 8, 

 p. 147. (A., 1899.) 



938. EARTH, LONG DURATION OF 



Coral Reefs Require Vast Periods of Time 

 Contrasted Brevity of Human Life. The 

 evidence capable of being adduced from the 

 growth of coral reefs goes far to prove the 

 constant and uniform state of our earth 

 throughout immense periods of time. The 

 testimony of Mr. Dana with regard to the 

 rate at which coral grows is to the effect 

 that the massive corals on which the in- 

 crease of reef depends are of very slow 

 growth; the branching and certain other 

 kinds growing at a faster rate. One- 

 eighth of an inch per year is given by this 

 author as " the average upward increase of 

 the whole reef-ground per year"; and the 

 estimate appears to be a perfectly just one, 

 when judged by the evidence afforded us of 

 the rate of growth in corals. All authori- 

 ties agree in stating the growth of massive 

 corals at a very low rate, and the time which 

 has been occupied in the formation of a 

 reef 2,000 feet thick must, therefore, on Mr. 

 Dana's estimate, be set down at 192,000 

 years. This computation, it must be remem- 

 bered, is one dealing with the work of mod- 

 ern corals. In the far-back past, coral reefs 

 existed similar in every respect to their 

 modern representatives; these fossil reefs 

 in many cases evincing an immense thick- 

 ness. Hence we are led to believe that, not- 

 withstanding the alteration which our earth 

 has undergone, it has had prolonged periods 

 of rest; and the existence of a modern coral 

 reef may therefore afford evidence, not only 

 of the immensity of past time, but also of 

 the uniformity of Nature's ways and works 

 during periods compared with which the 

 farthest limits of history and even of man's 

 own age are but as yesterday. WILSON 

 Facts and Fictions of Zoology, p. 43. (Hum., 

 1882.) 



939. EARTH LOSING HEAT Change 

 and Upbuilding of Surface to Cease The 

 Planet's Old Age. The earth's nuclear re- 

 gions are parting with their heat, and as 

 they cannot part with their heat without 

 warming the surface-crust, which neverthe- 



less grows no warmer, we perceive that the 

 surface-heat is maintained from a source 

 which is being gradually exhausted. The fit- 

 ness of the earth to be the abode of life will 

 not only be affected directly in this way, but 

 will be indirectly affected by the loss of that 

 Vulcanian energy which appears to be one of 

 its necessary conditions. At present, the 

 surface of the earth is like the flesh clothing 

 the living body; it does not wear out be- 

 cause (through the life which is within it) 

 it undergoes continual change. But even as 

 the body itself is consumed by natural proc- 

 esses so soon as life has passed from it, so 

 when the internal heat of the earth, which is 

 its life, shall have passed away, her surface 

 will " grow old as doth a garment" (Ps. cii, 

 26) ; and with this inherent terrestrial vi- 

 tality will pass away by slow degrees the 

 life which is upon the earth. PROCTOR Our 

 Place among Infinities, p. 28. (L. G. & Co., 

 1897.) 



940. EARTH ONCE A MOLTEN MASS 

 There was a time when our earth was in a 

 state of igneous fusion, when no ocean 

 bathed it and no atmosphere surrounded it, 

 when no wind blew over it and no rain fell 

 upon it, but an intense heat held all its ma- 

 terials in solution. In those days the rocks 

 which are now the very bones and sinews of 

 our mother earth her granites, her porphy- 

 ries, her basalts, her syenites were melted 

 into a liquid mass. AGASSIZ Geological 

 Sketches, ser. i, ch. 1, p. 2. (H. M. & Co., 

 1896.) 



941. EARTH, THE FINISHING OF, 



FOR MAN The work of the artist is not 

 yet finished when his statue is blocked out 

 and the grand outline of his conception 

 stands complete; and there still remained, 

 after the earth was rescued from the water, 

 after her framework, of mountains was 

 erected, after her soil was clothed with field 

 and forest, processes by which her valleys 

 were to be made more fruitful, her gulfs to 

 be filled with the rich detritus poured into 

 them by the rivers, her whole surface to be 

 rendered more habitable for the higher races 

 who were to possess it. AGASSIZ Geological 

 Sketches, ser. i, ch. 7, p. 204. (H. M. & Co., 

 1896.) 



942. EARTH UNINHABITABLE 

 WITHOUT BIRDS Our Unconsidered In- 

 debtedness. If we were deprived of the serv- 

 ices of birds [in the destruction of insects], 

 the earth would soon become uninhabitable. 

 Nevertheless, the feathered protectors of our 

 farms and gardens, plains and forests, re- 

 quire so little encouragement from us in- 

 deed, ask only tolerance that we accept 

 their services much as we do the air we 

 breathe. We may be in debt to them past 

 reckoning, and still be unaware of their ex- 

 istence. CHAPMAN Bird-Life, ch. 1, p. 9. 

 (A., 1900.) 



943. EARTH'S ANCIENT COMPAN- 

 ION The Moon an Object of Unique Interest 

 to Man. The moon possesses for us an 



