STRATIGRAPHY OF BEORAFT MOUNTAIN 1 , COLUMBIA 



COUNTY, N. Y. 



With stratigraphic map and sections 

 BY AMADEUS W. GRABAU 



Introductory 



Becraft mountain, close to the city of Hudson, has been known 

 to geologists since the early days of geologic study in the State 

 of New York, and descriptions of it play an important part in 

 the early reports on the geology of the State. In a letter dated 

 Dec. 3, 1820, and published in Silliman's Journal for 1822 2 , Mr 

 John P. Jenkins, of Hudson N. Y., gave a brief description of 

 Becraft mountain. He calls it " . . . a solid mass of gray rock 

 supporting a blue compact limestone; the upper strata of both 

 rocks contain a great variety of petrifactions which have been 

 described by Mr Eaton and others." 



In 1823 Silliman described the " marble of Hudson," which 

 was wrought by Mr Charles Darling of that city. He considers 

 it of high class, and similar to that of the Peak of Derbyshire. 

 The " marble " is the Becraft limestone of Becraft mountain. 



Mather 3 in 1838 gives a description of the strata of Mount 

 Becraft and of Mt Bob, which lies a little to the north, as well as 

 their general structure, and states that the limestone of the 

 mountains lies unconformably on the Hudson river slates. In 

 1840 4 he compared the strata of the Helderberg mountains with 

 those of Becraft, considering them similar. In 1841 5 he again 

 refers to Becraft, emphasizing the unconformity between the 

 " nearly horizontal " Helderberg limestones, and the " highly 

 inclined " subjacent Hudson river strata. 



In his final report, 1843 6 , Mather describes Becraft mountain, 

 and gives three sections to illustrate the structure. The descrip- 



1 Topographically Becraft mountain would be considered a hill, since the 

 highest elevation on it is less than 500 feet above the sea. Structurally, how- 

 ever, it is a section of a mountain range. All the localities may readily be vis- 

 ited in a short walk from Hudson N. Y., where good accommodations may be 

 obtained at the Worth house, or in private boarding houses. 



2 Am. Jour. Sci. 1822. 4 : 33. 



8 Geol. N. Y. 1st Dist. 2d An. Rep't. 1838. p.165, 166. 



4 Geol. N. Y. 1st Dist. 4th An. Rep't. 1840. p.238. 



• Geol. N. Y. 1st Dist. 5th An. Rep't. 1841 d.90. 



6 Geol. N. Y. 1st Dist. Final Rep't. 1843. p.344-52, pi. 24, fig. 4-6. 



