366 PETROLOGICAL ABSTRACTS AND REVIEWS 
As T. W. Richards has anew and most felicitously stated the principle 
which should guide us as petrologists, “‘The soundness of all important 
conclusions of mankind depends on the definiteness of the data on which 
they are based". «2 The more subtle and complicated the conclusions 
to be drawn, the more exactly quantitative must be the knowledge of 
the facts.’”? 
It may be well to anticipate somewhat by noting that the generaliza- 
tions particularly questioned by the present writer are the existence of 
the alkaline and calcic branches of igneous rocks and the correctness of 
various forms of statement concerning their distribution on the earth, 
their genetic and tectonic relations. The first-named and most popular 
conception rests almost wholly on the strongly marked and contrasting 
characters of certain very different series or families of rocks. It has 
never been justified by thorough and unbiased study of the host of 
intermediate series. 
In the discussion of geographic distribution Harker first refers to the 
commonly accepted generalization of petrographic provinces. Few, if 
any, petrologists question the fact of the petrographic province. But 
few provinces have thus far been so thoroughly investigated that we 
know the full range of rocks occurring in them, their composition, and 
occurrence. The best known provinces are ones of strongly marked 
characters, as a rule. 
The main theme of the address is, however, not the limited problem 
of the petrographic province but rather that of the two great hypothetical 
branches of igneous rocks variously called Atlantic and Pacific, alkali 
and subalkali, alkalic and calcic, etc. In the ‘Natural History of 
Igneous Rocks” Harker used the first named terms but here substitutes 
“alkaline and calcic.’’ This division is referred to as ‘““now becoming 
recognized as the most fundamental distinction to be made among 
igneous rocks”’ and our author’s principal topic is, in fact, the broad 
relationship of these branches to the nature of tectonic movements in the 
earth’s crust and the genetic significance of this relationship. 
Such an address is not the place for details of fact, yet the layman 
and general geologist listening to this discussion must have been misled 
by the positive form of several generalizations made by Harker. Some 
of these are qualified, it is true, but so grudgingly and inadequately as 
to minimize the effect. 
While no one has yet attempted a thorough and fair definition of the 
alkaline and calcic branches, Harker refers to their characters as ‘‘too 
' Faraday lecture, Science, XXXIV (1911), 538. 
