]\Iarylaxd Geological Survey 47 



geological reports of the State. He divided the rocks of the entire State 

 into 24 divisions, some of which were again divided, and each one was 

 called a formation. In general the formations extending into Pennsyl- 

 vania and Xew York were correlated with the formations of those States, 

 the Pennsylvania name being given first, followed by that of the New 

 York reports. Those now included in the Devonian System are as follows :. 

 Formation No. 15a, Pre-nieridian limestone of Pennsylvania, Lower 

 Helderberg of Xew York; formation No. 15b, Meridian series of Pennsyl- 

 vania, Oriskany sandstone of New York; fonuation No. 16a, Cadent 

 slates and shales of Pennsylvania., Marcellus slate, Hamilton group and 

 Genesee slate of New York; formation No. 16b, Vergent series of Penn- 

 sylvania., Portage flags and Ithaca and Chemung groups of New York 

 and formation No. 17, Ponent series of Pennsylvania, Catskill group of 

 New York. It also contains the first colored geological map of Maryland 

 on which is shown the distribution of the different formations. There are 

 three colors for what is now recognized as Devonian, the Pre-meridian and 

 Meridian being grouped together as No. 15, the Cadent and Vergent as 

 No. 16 and the Ponent or Catskill as No. 17. There is also a structural 

 section extending from the western line of the State due east to Hancock 

 and thence southeast to Chesapeake Bay. 



Hall in volume iv of the Palseontology of New York, published in 1867, 

 reported eleven species of brachiopods from the Hamilton of Maryland. 

 Most of the succeeding volumes of this great work have contained de- 

 scriptions and figures of new species from the Maryland Devonian, figures 

 of Maryland specimens or reported the occurrence of other species in that 

 State. 



In 1876 Mr. Jed Hotchkiss published a work on Virginia containing 

 a colored geological map of Virginia and West Virginia, which had been 

 colored by Professor Wm. B. Eogers in 1873. The Devonian rocks are 

 shown by a single color; but apparently only formations VIII and IX are 

 referred to this system. 



In 1880 Mr. Howard Grant Jones published a paper on the Cumber- 

 land or Potomac Coal Basin containing a section from the Lower Barren 

 Measures down to what he called the Pocono sandstone. This section 



