NATURE STUDY. 



PUBI^ISHED UNDER THE AUSPICES OF THE 



Manchester Institute of Arts and Sciences. 



Voiv. III. May, 1903. No. 12. 



Tipping Rocks. 



Among the most interesting relics left by the ice age are 

 the tipping rocks, large bowlders poised so evenly and 

 balanced so nicely upon the ledge below that they can be 

 rocked, sometimes by the hand alone. These huge rocks 

 were in some cases let down gently by the melting ice and 

 chanced to rest upon an angle that would allow the slight 

 rocking of a mass weighing perhaps hundreds of tons. 



It is probable that in some rocks weathering has been 

 the cause of this phenomenon. The portions of the rock 

 resting rather lightly against the ledge below would be 

 kept constantly moist and thus would decay faster than 

 those parts that dried more quickly or that portion where 

 the pressure of the entire mass would prevent to some ex- 

 tent the entrance of water and the gases of the atmosphere. 



Sometimes a bowlder that has been split by frost has 

 one of the fragments nicely enough balanced to be rocked 

 by the application of human strength. This adds to its 

 uniqueness, for while it all happened so, it is happenings 

 that make curiosities. A rocking bowlder of this latter 

 class is the tipping rock of Shirley Hill in Goffstown, N. 



