184 THE POPULAR SCIENCE MONTHLY. 



to persist unless carefully aided by artificial selection, yet they 

 must have commenced as acquired characters. Well-broken horses 

 and well-trained dogs transmit these qualities to their offspring, 

 and all domestication and cultivation of animals and plants, all 

 changes wrought in them by man, must have been first acquired 

 to some degree, and then, by intelligent selection, the degree can 

 easily be increased. Like produces like, and if we can not ex- 

 plain why, it is because we have not yet solved the problem of 

 heredity. The elaborate theory offered by Prof. Weismann in his 

 Germ-Plasm, plausible as it sometimes seems, true as it doubtless 

 is in many of its details, utterly fails to solve this problem. It is 

 altogether too rigid, too mechanical, to explain such subtle 

 phenomena. Nature is more flexible, more self-adjusting, more 

 delicate than his system contemplates, and is constantly doing 

 just those things which he insists can not be done. 



I trust that it has been sufficiently shown, chiefly from his 

 own words, that in elaborating this complicated theory Prof. 

 Weismann, guided, as he always seems to be, by the highest re- 

 gard for truth, has, greatly to his credit, conceded all the essential 

 points in the long controversy as to the inheritance of acquired 

 characters. The discussion may therefore be regarded as nar- 

 rowed down, not so much to the relative importance of the direct 

 and indirect factors, as to the degree to which in any given case 

 the one or the other has operated in determining the observed 

 result. 



THE CINCINNATI ICE DAM. 



Bt 6. FEEDEKICK WEIGHT, 



PE0FES90R OF THE HAEMONY OF SCIENCE AND EEVELATION IN OBEELIN COLLEGE. 



IN many respects the Ohio is one of the most remarkable rivers 

 in the world. Its drainage basin comprises about two hun- 

 dred thousand square miles on the northwestern slope of the Alle- 

 ghany Mountains. Its eastern tributaries rise at an elevation of 

 something over two thousand feet above the sea, and hence are so 

 situated as to carry the rainfall and the melting snows with great 

 rapidity into the main channel, which at Pittsburg is seven hun- 

 dred feet above the sea, and at Cairo, where it unites with the 

 Mississippi, about three hundred feet ; the descent from Pittsburg 

 to Cairo being about four hundred feet in a distance, as the river 

 runs, of nearly a thousand miles. 



The whole course of the river is through sedimentary rocks, 

 which, though of Palaeozoic age, have been but slightly disturbed. 

 The elevation of the region has been so continental in its propor- 

 tions that the rocks have retained to a great degree their original 



