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178 



NEW YORK STATE MUSEUM 



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- 

 3 ment of certain cleavages ; that is, where 

 = one of the characteristic cleavages at an 



- angle to the bedding plane is well devel- 



1 oped, erosion can most advantageouslv 

 H attack it. 



2 The present paper gives a report on 



- the succession of faunas in the strata of 

 ^ Trilobite mountain, from the Manlius to 



3 the Onondaga formation inclusive. Most 

 I of the field work was done during the 

 5 summer of 1902, while the work on the 

 ? collections was carried on durino- 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. 



A 



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