Maryland Geological Survey 89 



been subdivided into three parts by Clarke and Lnthcr," wlio have des- 

 ignated them the Maroellus shale, the Stafford limestone, and the 

 Cardiff shale, corresponding to the lower shale, the upper limestone, and 

 the upper shale respectively. 



Clarke ^ has shown that the Onondaga and Maroellus do not represent 

 strictly successive periods of time, but tliat the lower beds of the Marcellus 

 were deposited contemporaneously with the upper beds of the Onondaga, 

 limestone being formed to the west farther from the shore, while the 

 clays were deposited simultaneously in the east nearer the shore. This was 

 proved by tracing the Goniatite limestone westward until it finally 

 merged with the upper bed of the Onondaga limestone due to the thin- 

 ning and ultimate disappearance of the black shales which lie between 

 it and the Onondaga, in central New York. In other words, the lower 

 beds of the Marcellus and upper beds of the Onondaga are contem- 

 poraneous and re])iosont not two periods of time, but two phases of 

 sediments deposited simultaneously but under different conditions. It 

 thus becomes impossible to speak of Marcellus time as successive to Onon- 

 daga time, precisely as it is impossible to distinguish Chemung from 

 Catskill time. 



The Goniatite limestone, which is the important horizon-marker, is 

 distinguished by the presence of numerous goniatites, particularly Ago- 

 niatites expansus, Avhich is its most diagnostic form. The latter species 

 is sometimes said to occur both in the Onondaga and the Marcellus, but 

 it is to be noted that these terms may signify only the same horizon. The 

 Stafford limestone which occurs at a higher level in the Marcellus is 

 characterized by the advent of numerous species of Hamilton affinities 

 which mingle with those of earlier age. It thus becomes a suitable hori- 

 zon for a formational division as proposed by Clarke. 



It would not be surprising to find that the shales replace succes- 

 sively lower and lower limestone beds as we approach the shore line until 

 a large part of the deposits of Onondaga time may be represented by 

 shale. Such appears to be the ease in Maryland. 



^BulL N. Y. State Mus., No. 63, 1902, p. 16. 



'' Clarke, J. M., BulL N. Y. State Mus., No. 49, 1901, pp. 115-138. 



