10 NEW YORK STATE MUSEUM 



which range in time from the base of the Paleozoic to the upper part 

 of the Ordovicic period. Northeastward these rocks extend into 

 Massachusetts and Vermont and southwestward into New Jersey, 

 Pennsylvania and beyond. 



Within the quadrangle they are of considerably lower average 

 elevation than the gneisses of the mountains. This reduced eleva- 

 tion is believed to represent the erosion that has taken place in 

 these rocks below the Cretacic level after the peneplain had been 

 elevated at the close of Cretacic time. 



So far as now known, these younger strata have no later rocks 

 older than the Quaternary overlying them within the limits of the 

 quadrangle. 



PREVIOUS GEOLOGIC WORK 



Because of the extensive geographic development of these rocks 

 and their difficult geology there has appeared, during the last fifty 

 years or more, a large body of literature dealing with them through- 

 out their length and breadth. The work has been carried on under 

 the auspices of State and federal surveys and by private enterprise. 

 Work within this quadrangle was undertaken early in the history 

 of serious geological investigation in this country. 



In 1843 W- W- Mather submitted his quarto report on the Geology 

 of the First District of the State of New York. This dealt 

 with southeastern New York and was the first important contribu- 

 tion bearing on the geology of this area. With the exception, per- 

 haps, of an excursion by Sir William Logan and James Hall in 1864, 

 which resulted in the assignment of the younger rocks of this and 

 neighboring areas to Logan's Quebec Group, and which introduced 

 much confusion at the time, no other important contribution was 

 made until 1878. 



In that year T. Nelson Dale discovered fossils in the slates at 

 Poughkeepsie. The fossils were a'ssigned by Hall to the " Hudson 

 River Group." The find attracted the attention of Professor J. D. 

 Dana to the strata of southern Dutchess county. This eminent 

 geologist, what the time was working at the difficult stratigraphy 

 of western Massachusetts and the neighboring portion of New 

 York State, now traced the limestones from the north to the Hud- 

 son river, discovered fossils in them at Pleasant Valley, and dis- 

 cussed their general geologic significance. 



Apparently through the influence and encouragement of Dana, 

 Professor W. B. Dwight began his fruitful investigations in the 

 Wappinger limestones of Dutchess county. Professor Dwight's 

 papers were published at intervals from 1879 to 1900. His investi- 



