Page:The Scientific Monthly vol. 3.djvu/596

 S90 THE SCIENTIFIC MONTHLY

and afforded a shelter from heat, cold and storm, and a barrier to ene- mies. While man has since learned the manufacture and uses of other materials, he still seems to place his greatest faith in stone as a means of combining dignity, utility and permanence. The most famous and nearly the most ancient stone monuments are the Pyramids of Egypt. They have endured so long as to seem almost indestructible. But let the climatic conditions be altered to correspond with central Africa, or even the interior of the Sahara, and the Pyramids would be much less able to resist the forces of nature; their period of duration would be greatly shortened. Earthquake is perhaps the greatest destroyer of structures in stone, yet man has learned how to build, if he will, so as to withstand even violent earthquake shocks, as evidenced by the won- derful mortarless masonry of the Incas, in Peru, a land that certainly can not be said to be free of the peril of earthquake. Beinforced con- crete is probably the best modern material that might be used to with- stand earthquake shocks. The concrete work at Panama, a region that has seen considerable seismic disturbance, will probably afford us in- formation as to its stability in due time.

It might be remarked in this connection that reinforced concrete seems to suffer but little from the effects of fire, unless the heat be exceptionally intense and prolonged. Many rocks, however, do not pass the ordeal of fire without becoming thereby more readily attacked by weathering agents. Granite, marble, limestone and sandstone, four of the most used building stones, endure heat rather imequally. Both marble and limestone are decomposed by heating, passing into ordinary lime. Digressing for a moment to the use of marble in ancient art, we are frequently struck by the lack of foresight, or of knowledge, of the ancient as well as medieval and some modern sculptors in choosing marble as the final expression of their art. Pure white marble is un- doubtedly beautiful; but, supposing some vandal desires to satisfy his appetite for destruction by pulling down marble statues, shattering them by blows, or forever destroying them by fire? Modern artists never cease grieving over the incompleteness of many of the ancient masterpieces, known to us only in a fragmental or damaged condition.

Granite and sandstone may successfully withstand earthquake and fire, but they, as well as less stable rocks, can not be entirely free of the effect of vulcanism. The well-known effect of molten lava upon sand- stone, changing it to quartzite, would be the final chapter in the his- tory of an edifice of sandstone, overtaken by a lava fiood. And in the case of either granite or sandstone, a lava flood would so fill and sur- round and alter the structure that it would be as good as lost forever. The earthquake and volcano belts of the earth have been carefully traced and defined, and are found to be practically identical in posi- tion. The association of earthquakes with volcanoes is very striking; but are we quite certain that these belts will always remain as they

�� �