1887.] IfEW YORK ACADEMY OF SCIENCES. 79 



human race, than those which relate to rainfall and the reflux of 

 the condensed waters of the sea. The causes which determine 

 the quantity of rain which falls in any region are various : ocean 

 currents, aerial currents, mountain ranges, extended valleys and 

 plains — all produce their effects; and, although the most 

 varied extremes occur of regions where vegetation is luxuriant 

 on the one hand, and where deserts exist without rainfall on the 

 other, yet such is the constancy of nature in her great cycle of 

 changes, that each place receives its appointed share almost un- 

 changed from year to year. 



The average rainfall of a region is, therefore, in most civilized 

 countries, one of the best established of all meteorological phe- 

 nomena. 



It is not so, however, in regard to the return of the waters to 

 the sea. The flow of surface streams may, it is true, be deter- 

 mined with approximate accuracy, and their courses are well de- 

 fined ; but the disposal by nature of that large part of the rain 

 which does not appear in the rivers and brooks, as they accumu- 

 late in magnitude toward the sea, is involved in much obscurity. 

 A portion of the condensed vapors is known to be absorbed by 

 plants, and a portion is reevaporated, but a still greater part, 

 apparently, disappears beneath the earth^s surface. By what 

 precise channels this large volume of water ultimately reaches 

 the ocean, how much of it enters the covered out-crops of 

 porous strata and, finding its way deep into the earth's crust 

 between underlying and overlying consolidated beds, is ulti- 

 mately discharged underneath the waters of the ocean ; how 

 much enters faults and fissures, and again issues in springs of 

 pure or mineral waters; how much is concerned in excavating 

 underground courses through or among the softer or more 

 soluble rocks, or follows channels already thus excavated, is not 

 and cannot be known. But that no inconsiderable portion of 

 this subterranean flow follows more shallow channels in the 

 loose detritus upon the surface seems probable. In most coun- 

 tries where the rainfall is copious, moderate excavations at the 

 surface reveal the presence of water. In our own country every 

 farm has its well, whether it be situated on a hill or in a valley ; 

 and, while these wells occasionally become dry in very dry years, 



