312 BULLETIN OF THE 



E. Emmons. Agriculture of New York. Albany, 1846. "Vol. I. 

 pp. 134-175, and Plates IV., XX., and XXI., bear more or less directly 

 on the structure of our district. 



N. S. Shaler. On the Existence of the Alleghany Division of the 

 Appalachian Range within the Hudson Valley. American Naturalist, 

 XL, 1877, 627, 628. A short notice of the extension of distinct anti- 

 clinal and synclinal structure to this point. 



W. M. Davis. The Little Mountains* east of the Catskills. Appa- 

 lachia, III., 1882, 20-33. A detailed elementary account of the struc- 

 ture of a small part of the Helderberg belt ; with map and sections. 



No geological maps of this region have been drawn on a large enough 

 scale to show anything more than parallel strips of color along the west- 

 ern side of the Hudson valley. The little sketch-map in the last of 

 the above-named articles, and the map accompanying this paper, are the 

 first that show the well-marked Appalachian topography of the district. 



The material for the present paper was obtained in part during two 

 short visits in the spring and summer of 1877, the first in company with 

 Mr. E. R. Benton, now Professor of Natural History in the L^niversity 

 of Rochester; the second with Professor N. S. Shaler, Mr. J. S. Diller, 

 and members of the Harvard Summer School of Geology. But a third 

 trip made in the spring of the present year furnished fuller results ; in 

 this I was accompanied by Mr. J. E. Wolff, Assistant in Geology, and by 

 Messrs. Bunker, Chase, Clark, Dean, and Jackson, students in Harvard 

 College and the Lawrence Scientific School. To all of these I desire to 

 give thanks for aid in making the observations herein i-ecorded. 



Our work was mostly stratigraphical, and some description of part of 

 the results has already been published in Appalachia, as above men- 

 tioned. As only a short time was spent on the ground, the reader must 

 expect to find some points indicated as probable, but not fully estab- 

 lished ; many of these would afi'ord excellent subjects for detailed sum- 

 mer studies, and I should be greatly pleased to learn of their being taken 

 up by residents or summer visitors. 



The Silurian and Lower Devonian strata occurring in this part of the 

 Hudson valley are the Hudson River sandstones and shales in the low 

 country on the east by the river, and in occasional anticlinal valleys 

 within the Little Mountain belt ; next, the Lower Helderberg limestones, 

 in good variety and well exposed at many points ; over these the grits 



* This name was given by the writer to call attention to the peculiarly mountain- 

 like structure and form of these limestone hills. They are not so known in their own 

 neighborhood. 



