278 R. T. HILL — PELE AND THE WINDWARD ARCHIPELAGO 



mechanisms leading up from the unknown interior of the earth, and even 

 these studies must be carried on at a respectable distance when the vol- 

 cano is at work * 



The chief result of studies under such unfavorable conditions has been 

 to ascertain that the vent holes discharge at the earth's surface nearly 

 every known chemical element in various combinations and forms — 

 solids, liquids, and gases. These materials in the condition in which 

 they reach the surface — for they convey but little idea of the conditions 

 within the interior from which they have evolved — represent exhausted 

 and completed products of nature's workshop within. 



The concentration of our studies on these erupted products, together 

 with the security in which we inhabit the earth's surface, has led many 

 to regard the world as a completed or finished object, while in fact it is 

 a living mechanism containing within itself forces and material capable 

 of great chemical work like that so obvious in the sun and some other 

 stellar bodies. Thus it is that purely geological studies of volcanoes have 

 resulted chiefly in the presentation of numerous and confused systems 

 of classification of the apparently infinite varieties of igneous rocks, which 

 all students now admit to be but the varied manifestations of the one 

 great material substance of the interior of the earth. It is at least dis- 

 couraging to learn, after twenty-five years of collecting, slicing, and micro- 

 scopically studying volcanic rocks, that petrographers have recently de- 

 creed that " there are no well defined chemical groups of rocks, but rather 

 a continuous series with no natural divisions," f thus admitting that the 

 various forms of crystalline rocks as we see them in their cooled condi- 

 tion are but the differentiated products of a mother substance from which 

 they have all evolved. 



The geologist, notwithstanding all his studies of the earth's crust, its 

 marvelous history and rearrangement of material, likewise admits that 

 the great changes of level, such as the upheaving and subsidence of land 

 and continents, are explicable by no known superficial agency, and real- 



* The field and laboratory geologists' opportunities for interpreting volcanic phenomena have 

 many limitations. Their observation of the vital phenomena are as restricted as those of a man 

 who endeavors to ascertain the great reactions which take place within a roaring furnace by dis- 

 tantly observing the escaping smoke from its cupola and studying the cold slag of its dump pile. 



They can only see the superficial and relatively secondary phenomena of volcanoes— the top 

 of the chimney— for nature has never exposed the deeper internal mechanism to view, or, at most^ 

 a shallow depth of what was formerly the underground portion of dead volcanoes, frequently 

 exposed by erosion, showing a east, so to speak, of some of the old rock material. 



Traces may also be seen of what are called the "expiring after effects of vulcanism," such as 

 dikes which push upward into the old cone or overburden as the cooling vents clogged, or deposits 

 of copper, silver, gold, sulphur, and other metals which have either evolved from the great proto- 

 magma during the expiring after moments, and filled veins and fissures, or which were differen- 

 tiated like the other elements of the rocks from the cooling magma into distinguishable ore segre- 

 gations (pegmatitic) before being still further collected into more concentrated ore bodies by the 

 subsequent circulation of atmospheric waters. 



flddings, 1904. 



