APPENDIX. Ill 



cealed by a thin film of ice which is generally formed over the 

 exposed water surface, slip into the water and lose their lives. 

 Such accidents are common, though not often fatal. The horse 

 is generally choked by a strap round his neck to stop his strug- 

 gles, and while thus quieted he is dragged out by the efforts of 

 the driver, and soon recovers on the slacking of the strap. 



When the edges of the ice rise a passage is hewn by means of 

 an axe. Looking at the Appalachian section of Mr. Lesley, it 

 seemed to me that a section of these iqe fields was a model, on a 

 small scale it is true, yet several miles in length and width, of the- 

 rock strata which are there represented. 



The same solid field floating upon a liquid ocean of constant or 

 nearly constant temperature, exposed now on its upper surface to 

 the atmosphere and to empty space, but at some former time 

 covered by many thousand feet in thickness of ice, which ha.s- 

 eroded the ridges and filled the valleys ; iu some places crimped 

 by an evident increase in dimensions, in others forced up into 

 ridges or depressed into valleys, anticlinal and synclinal axes, 

 but these greater disturbances occupying only 175 miles of a 

 cross section or profile 3000 miles in length. 



The filling of the ice cracks by water which freezes is repre- 

 sented by the dykes of igneous or aqueous rock which abound in 

 the geological profile. All these entered in a fluid condition, 

 then solidified, and increased the dimensions of the field or forma- 

 tion. 



Changes of temperature, not diurnal as in the ice fields, but 

 secular, would produce the ridges and valleys in the rocks as the 

 diurnal changes produce their models in the ridges and gutters of 

 the ice fields. 



It is well to look for the smallest sufficient cause in reasoning 

 upon observations of natural phenomena ; and as Lyell holds that 

 most of ihe changes on the earth's surface may be accounted for 

 by causes and operations still seen in action, I have thought it 

 worth while to record these observations, forced upon my attention 

 during my daily rides for two seasons upon a frozen lake, as illus- 

 trating and accounting for a part of the contortions of the earth's 

 surface. 



Some sketches on the accompanying page illustrate the more 

 common physical phenomena herein described. 



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