Processes and their Results. 377 



balance. For example, the abnormally symmetrical calcareous 

 ooncretions, though very curious and though beautifully illustrated 

 in figs. 371-373, are not of sufficient geological consequence to 

 deserve the two pages of the textbook devoted to them, and the 

 same remark applies to the septarian nodules, figs. 375-377, while 

 such an important feature as the igneous dyke is illustrated by 

 a sand-filled fissure which is not a true dyke. 



In the statement on p. 478 — "Since the strike is always at right 

 angles to the dip, the strike need not be recorded if the direction of 

 dip is. Thus dip 40°, S. 20° W. is the same as dip 40°, strike 

 W. 20° N." — it seems to be forgotten, in the last sentence, that the 

 dip may be away from the strike-line in two directions. The 

 definition of an isoclinal fold takes the form of a simple reference to 

 a figure (fig. 393), which shows the beds folded vertically — surely 

 a misleading and insufficient definition for the student ! We 

 thought that the term ' pitch ' had been introduced and adopted in 

 America to express the inclination of the crests and troughs of folds ; 

 but we find on p. 483 that a circumlocution, introducing the word 

 * plunging,' is used in this sense. 



In the next chapter (ix, pp. 502-562) on "The Movements and 

 Deformations of the Earth's Body (Diastrophism) " the authors 

 again take a stimulative plunge into the philosophical aspects of the 

 science. Earthquakes and their effects are discussed at some 

 length ; and then the ' slow massive movements ' are brought under 

 consideration, including the 'nearly constant small movements' or 

 gentle warpings, the ' great periodic ' or ' mountain - forming ' 

 movements, and the ' plateau-forming ' and ' continent-forming ' 

 movements. Some suggestive ideas are broached in comparing the 

 relative values and effects of these various deformations ; and then 

 we are carried deeply into hypothetical physics in speculating upon 

 the causes of movement and the probable condition of the earth's 

 interior. In this, and in the following chapter (x, pp. 563-607) 

 on " The Extrusive Processes," free play is given to the method of 

 ' multiple hypotheses ' already alluded to ; and among these 

 hypotheses the theory of the growth of the earth by solid accretion, 

 recently brought forward by the senior author, receives full con- 

 sideration and leads to the introduction of some novel ideas, whose 

 appraisement must be left to the physicist. He will be a tough 

 student, and far removed from the average hammer-wielder, who 

 shall set himself conscientiously to fathom the profundity or other- 

 wise of these speculations. 



The discussion of terrestrial vulcanism (with a side-glance at the 

 mountains of the moon) includes a description of the different types 

 of eruptive activity and their products ; and it closes with a review 

 of seven different hypotheses, arranged under two leading assump- 

 tions, as to the origin and mode of extrusion of lavas and their 

 accompanying gases, the theory of accretion here receiving further 

 development. 



The final chapter (xi, pp. 608-641), dealing with "The Geologic 

 Functions of Life," embraces a brief statement of Professor 



