THE EVOLUTroN OF PETROLOGICAL IDEAS. 289 



ical liistoiy. AriiK-h:iir philo8<)[)liizing', apart from actual woi-k in the, 

 field, the hiboratorv, and the museum, is by no means to be com- 

 mended. But the worship of fact, as fact, may easily be overdone. 

 The num])er of discoverable facts is practically intinit(\and it is there- 

 fore possible to get into such a condition as not to Ije a])le to see the 

 wood for the trees, to lose the due sense of proportion, and to become 

 mere machines for tal)ulatino- intermina))le trixialities. 



On the other hand, it should ])e remembered that every worker 

 endowed with imagination nuist fornudate, in his own mind, man}^ 

 theories that will not stand the test of verification, and that it is quite 

 unnecessary for him to trouble other workers with such theories. lie 

 can test them for himself, and relegate them to oblivion if necessarv, 

 without l)urdening our overcro^^ded bookshelves with crude specula- 

 tions and unverihed hypotheses. 



It is only when a th(H)ry has proved its usefulness as a coordinator 

 of fact that it becomes worthy of the dignity of pul>lication. It mav 

 be true or false, most likely the latter; l)ut if it coordinati^s more facts 

 than anv other it is at any rate useful and may be conveniently retained 

 until replaced 1»y a Ix'tter. Controversy as to the truth or falsity of 

 a theory often seems to me l)eside the mark, for if a given theory coor- 

 dinates more facts than any other it is at least worthy of respect, and 

 niay be tentatively held as a Avorking hypothesis, along with the con- 

 viction that it is not true, or only partially true. Indeed, the contro- 

 versial spirit is. in my judgment, inimical to the best interests of 

 science. It makes a man more eager to refute than to understand the 

 views of his opponents: it tends to check the flow of sympathy, and 

 thus often ^jrevents that friendly cooperation which is so desirable in 

 the interest of scientific progress. When controversy becomes acute, 

 I alwa3's feel inclined to exclaim "'a plague on both your houses." 



Ever}^ branch of our man\"-sided science has l>enefited l)y the zeal 

 for collecting facts which manifested itself during the earl}' vears of 

 the nineteenth century. ^Methods of observation have been perfected, 

 national survej's and private individuals have examined and are exam- 

 ining- the geological structure of every civilized State, and explorers 

 have penetrated to almost every <[uarter of the globe. Our li))raries 

 and nmseums are being rapidly filled with records of all this scientific 

 activity. Side ])y side with the registration and cataloguing of facts 

 there has taken place an evolution of scientific ideas, and it is on this 

 aspect of the subject, so far as my own special branch is concerned, 

 that I propose to offer a few remarks. 



Rocks may be studied from two more or less distinct points of view, 

 the descriptive and the aetiological. But it is well to note that the 

 distinctness of these two points of view is but the expression of our 

 ignorance as to.the genetic relationships of the different types. Facts 



SM 1902 19 



