114 The Lo-v\^r Devonian Deposits of Maryland 



Correlation with New York. — Different problems are presented in 

 considering the correlation of the Helderberg of Maryland with the for- 

 mations east and west of the Helderberg Mountains of New York. These 

 areas are therefore considered separately. 



Correlation until Formations East of the Helderberg Mountains. — The 

 Lower Devonian and Upper Silurian strata pass, without modification, 

 from northern New Jersey into southeastern New York. In approaching 

 Eondout, New York, however, the lower formations undergo a change 

 accompanied by an increasing development of cement beds leading to the 

 discrimination of new formations. Clarke and Hartnagel recognize the 

 following sequence in the vicinity of Rondout.' 



Devonian Coeymans 



'Unconformity 



Manlius 



Rondout 

 Silurian -I Coblesklll 



Rosendale 



Wilbur 



Binnewater 



Ordovlclan /Unconformity 



I^Normanskill 



The Coeymans, Manlius, and Rondout are clearly the same as the corre- 

 sponding formations of northern New Jersey so that their correlation 

 needs no further consideration here. Divergent views have, however, been 

 held covering the relation of tlie Decker Ferry to the formations of New 

 York. 



Weller ^ correlated the Decker Ferry of New Jersey with the Coblesldll 

 of New York, basing his conclusion upon the evident similarity of their 

 faunas. Hartnagel ' who studied the subject somewhat later, restricted 

 the name Decker Ferry to the two lower zones of Weller's formation and 

 correlated them with the Rosendale and Wilbur of New York. He named 

 the coralline zone of Weller's Decker Ferry the Cobleskill, correlating it 

 with the formation of that name in New York and considered the 15 feet 



'N. Y. State Mus., Handbook No. 19, 1912, Table 2. 

 ^Tal. N. J., vol. ill, 1903. 



= Rept. N. Y. State Paleontologist for 1903, N. Y. State Mus., 57th Ann. Rept., 

 1905, vol. i, pt. i, pp. 348-349. 



