REVIEWS. 857 



should bear in mind that like every other method it has limitations 

 which the author does not fail to recognize. The most important of 

 these seem to be the following: (1) Our observations of phenomena 

 are often very limited. In spite of the numerous expeditions and deep 

 sea dredging how small a fraction of the whole territory has been 

 explored ; (2) an important difficulty arises from the scattered condi- 

 tion of the literature of the subject which has been already greatly 

 reduced by the present compilation ; (3) more vital is the difficulty of 

 studying forms which have no living representatives as the graptolites 

 and the blastids and the fact that in general the farther back we go in 

 geologic time the more difficult does it become to apply the ontologic 

 method ; (4) the most important limitation to this method, however, 

 arises from the assumption which lies at the very root of it, namely, that 

 factors affecting organic life and inorganic movement have remained 

 the same in all ages. Can we be certain that the oyster now com- 

 monly found in from one to two hundred and fifty feet of water lived at 

 the same depth in the Jurassic, or can we be sure that new factors have 

 not entered in or old factors been lost which affected the mode of life 

 and the deposition of strata ? It becomes necessary then for the onto- 

 logically working historical geologist to be keenly alive to these possi- 

 bilities of error and search in all his work to reduce the probable 

 error to a minimum. If approached in this spirit this last objection 

 would not prove as formidable as might at first be supposed and will 

 decrease as our knowledge of the taws of earth- history become more and 

 more complete. 



Proceeding to the body of his theme the author agreeable to the 

 nature of the ground to be covered divides his work into the study 

 (1) of the formation of rocks, especially the sedimentary ones, (2) the 

 mode of life of the marine organisms, and (3) the relations of the 

 first to the second or the outside conditions of life and their effect 

 upon the organisms (Bionomy) ; though for conventional reasons 

 these topics are taken up in the reverse of this their more natural 

 order. 



Under the title "Bionomy of the Ocean" the author considers the 

 distribution and conditions of life of marine organisms. As plants alone 

 have the power to organize inorganic substances, it is important that we 

 first study their conditions of life. They need light, water, carbonic 

 acid, and chromophyll, without which the processes of assimilation can- 

 not take place. As experiment has shown that light waves capable of 



