178 



NEW YORK STATE MUSEUM 



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occur in all horizons but are specially 

 characteristic of the Esopus, lends color 

 to this supposition. These hogbacks, 

 however, appear to be better explained 

 as the result of differential erosion, as 

 noted above. The more or less sudden 

 rise and dying away of such a ridge in. 

 its northeast-southwest trend is appar- 

 ently due to the greater or less develop- 

 ment of certain cleavages ; that is, where 

 one of the characteristic cleavages at an 

 angle to the bedding plane is well devel- 

 oped, erosion can most advantageously 

 attack it. 



The present paper gives a report on 

 the succession of faunas in the strata of 

 Trilobite mountain, from the Manlius to 

 the Onondaga formation inclusive. Most 

 of the field work was done during the 

 summer of 1902, while the work on the 

 collections was carried on during the 

 summer and fall of 1903 in the labora- 

 tory of Columbia University. In the 

 field work, great care was taken to dis- 

 tinguish between beds of varying lithic 

 or faunal characters, by keeping separate 

 the fossils collected from each, even 

 though such differences were noted in a 

 bed of less than an inch thick. 



The accompanying map and sections 

 were measured by pacing, and are sub- 

 ject to correction but in the acquisition 

 of the fossils great precaution was taken against mixing the collec- 

 tions from higher or lower beds. 



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