Mastodon Eemains in Ohio. 151 



mally short, as ISIr. Crnll supposes, it must in that case again obey the 

 same rule and trickle further down a mountain side than along an 

 almost horizontal valley. 



Obvious consequences of the theory propounded by Mr. Croll, such 

 as these, so directly opposed to all the phenomena of glacier motion, 

 seem effectually to bar the way to its reception, even as a plausible 

 theory. Some of Mr. CroH's papers upon geological subjects have been 

 of great value, but we fear his attempts to read one of the greatest if 

 not the greatest geological riddle of the present day has not been 

 successful. Nor do we think the full solution of the problem is possible 

 at present. Observations have not yet been sufficiently minute, 

 continuous or extensive, even in classic Switzerland, to enable the 

 cause of glacial movement to be detected. We do not yet know with 

 certainty the most important element in the question. The late Mr. 

 Wm. Hopkins deduced the swifter flow of the middle from the form and 

 position of the marginal crevasses, though contrary to the opinion of 

 Agassiz. But experiments have not yet proved whether the median 

 current of the glacier is in a condition of compression from pressure 

 behind or of tension from traction in front, or from both at different 

 places. Possibly this might be determined by the polariscope, but its 

 application is not easy, and no attempt has thus far been made in this 

 direction. The secret seems to be rather in the mass of the ice glacier 

 than in the other conditions. This was the convictiiMi of Agassiz, when, 

 in the conclusion of his great work on the "Glacial System of the 

 Alps," published in 1847, he says : '^ 



"The inclination of its bed is not the essential condition of the 

 motion of a glacier." 



"This motion is determined by its thickness rather than by its slope." 



Mastodon Remains in Ohio.— By John H. Klippart. 



In Ohio all the Post Tertiary formations are deposited upon the 

 strata found in Ohio, between and including the LoAver Silurian and 

 Upper Carboniferous. Many geologists doubt whether coal in Ohio 

 ever was formed west of the present boundary of this valuable min- 

 eral ; or, what is the same thing, they doubt whether the Ohio coal-fields 

 ever were continuous, and connected with those of Indiana and Michi- 

 gan. In many places in Ohio, the western extremity of the lower 



* Systems Glaciaire, p. 520. 



