1892.] prosser — the genesee section. 103 



Conclusion. 



Taking the sum of these maximum estimates, we have a series 

 of rocks 6810' in thickness between the base of the Olean conglomer- 

 ate and the top of the Archean (?). The same section compiled from 

 a series of well records gives a thickness of 7100'. This is probably 

 not a sufficient thickness for the entire section, since in the upper 

 part of the series it is very probable that the Chemung is thicker than 

 1 150', and possibly the Portage may have a greater thickness than 

 900'. It is interesting to compare this section with Hall's of 1838 

 and note what change has occurred in fifty-three years. It is hardly 

 possible to select a horizon in the upper part of the sections that is 

 precisely equivalent ; but it is thought that the stratum of "argill- 

 aceous iron ore" near Wellsville, at the top of the sub-division which 

 was later called Chemung, is not far below the horizon of the Wolf 

 creek conglomerate. The thickness of the series of rocks from this 

 stratum down to the mouth of the Genesee river, according to Hall's 

 section of 1838, is 4201'. The section compiled from well records, 

 allowing the same thickness — 300' — for the Medina on the Genesee 

 river as in Hall's section, shows that the same series has a thickness 

 of more than 4250'; but on account of our failure to yet obtain the 

 exact thickness of the Chemung and Portage it can not be stated how 

 much more than 4250' the total thickness may be. In the section 

 compiled from various sources of information this series has an esti- 

 mated maximum thickness of 4290'. However, the comparison of 

 the three sections shows that the early section of Professor Hall was 

 carefully constructed and, when the development of the science at 

 that time is taken into account, it reflects great credit upon the early 

 work of the veteran geologist and paleontologist of New York state. 

 The rocks above this " argillaceous iron ore " stratum up to the base 

 of the lowest coal at Instantur, Pennsylvania, Professor Hall esti- 

 mated to have a thickness of 1850', making the thickness of the entire 

 series from the base of the coal to the mouth of the Genesee river, 

 300' down in the Medina, 6051'. 



If this Genesee section be compared with the one of "Western 

 Central New York " (') it will be noticed that the probable thickness 

 of the series agrees much more closely with the estimated maximum 

 thickness than it did in the case of that section. This is due in a 

 measure to the fact that for the upper and middle parts of the Gene- 

 see section the estimated thickness agrees better with the actual thick- 



(1.) Am. Geol., Vol. VI, pp. 199-211. 



