7 88 THE POPULAR SCIENCE MONTHLY. 



rence of catastrophe and convulsion may be part and parcel of 

 uniformity itself ; and so in like manner, when the speculations of 

 Darwin have furnished the mechanists with renewed passion for 

 a new doll, Prof. Huxley has hoisted more than once a caution 

 signal. He has uttered a warning voice against converting a sci- 

 entific hypothesis into a dogmatic creed. 



It was high time. The passionate enthusiasm with which an 

 obscure and confused verbal metaphor has been accepted as solv- 

 ing all the mysteries involved in the origin of new forms of or- 

 ganic life, will one day be seen to have been what it is only 

 another great warning example of the impediments which beset 

 the progress of knowledge. That the origin of species may be 

 ascribed to some thing called " Nature " selecting things which did 

 not as yet exist, and could not therefore have been presented for 

 selection, is among those mysteries of nonsense which are not un- 

 common in the history of the human mind. But even this delu- 

 sion, prevalent as it has been, is breaking down, and assaults upon 

 it, all too timid though they be, are nevertheless increasing day 

 by day. I have therefore much sympathy with those who on the 

 whole are reasonably proud of geology as regards its past, and 

 are reasonably hopeful of it as regards its future. But its prog- 

 ress, and even our appreciation of its present teaching, is abso- 

 lutely dependent on two conditions : first, that we bear constantly 

 in mind the wide seas of ignorance which surround the little isl- 

 ands of our knowledge ; and, secondly, that we rightly estimate 

 the full sweep and significance of the facts and laws which we 

 can clearly see. It would be difficult to say whether the science 

 has suffered most from f orgetfulness of the things that we do not 

 know, or from failure to appreciate or exhaust the consequences 

 flowing from the things we do know. The vision of past worlds 

 which geology presents may be compared to the view of some 

 land seen at a distance upon the ocean, and upon which heavy 

 banks of cloud are resting. Above, mountains and peaks are seen 

 here and there, with outlines cut clear against the sky. Below, 

 capes and headlands and promontories are also seen, cut as clearly 

 against the sea. The middle slopes are only visible at intervals, 

 and some great plains just roughen the verge of the horizon. But 

 all details are lost. We do not even know whether we are looking 

 at one continuous land or at a group of islands. Hills which seem 

 united, or separated only by some narrow valley, may be really 

 far apart, and broad channels of the deepest water may lie be- 

 tween them. So it is with the vast landscapes of the past in the 

 revelations of geology. The general outlines of geological causa- 

 tion are clear enough ; and so in broad outline, too, is the general 

 succession of organic life. But both the exact history of the rocks, 

 and the exact history of the creatures which they entomb, are 



