386 BULLETIN OF THE NEW YORK STATE MUSEUM 



destruction of stone. The patter of the rain upon the soil 

 and the erosion by running waters, sculpturing the face of 

 the earth, are familiar phenomena to all. It also Is helped 

 by the dissolving property of the water, and the minute 

 exposed projections of the surface are sooner or later 

 loosened and carried away by the rain or the flowing cur- 

 rents of the little rivulets, which collect in the more rapid 

 dashes of our thunder-storms. Some of the more friable 

 limestones and marbles are examples of such combined 

 action of the dissolving and denuding rain. The little 

 structures reared by man are thus exposed to the same 

 forces as the gigantic cliffs and mountains about him, all of 

 which are being carried slowly but surely down to lower 

 levels and to the ocean. 



Perhaps equally potent as the water, but not so gen- 

 erally recognized, is the action of the wind, carrying sand, — 

 greater or less, according to Its velocity. On the seashore 

 and in exposed situations It is noticeable in the eroded sand 

 hills and cliffs. One of the most remarkable cases can be 

 seen In the dolomitic limestones of Dutchess county, near 

 Dover Plains, where the wind has sculptured the rocks in 

 fantastic forms over areas of several acres In extent. The 

 ground glass in the windows of some of the older houses at 

 Nantucket Is an example of wind work — natural sand blast. 

 The wind drives not only the sand, but the rain also, and 

 that Into every seam and joint, and penetrates often the 

 whole thickness of a wall, thus aiding the solvent action of 

 the rain-water. And, hence, the wear of the stone is great- 

 est on the sides of the prevailing winds. In New York 

 city, in the older churchyards, monuments are seen 

 smoothed on the windward side and the lettering effaced. 



Growing Organisms. — Confervae, algae, lichens and mosses 

 all thrive more or less upon ledges of rocks in favorable 

 situations. The effect of their growth on stone in a build- 

 ing is not altogether settled. 



We know that some of our hardest and apparently inde- 



