400 Scientific Intelligence, 



In 1817, Professor Eaton left Williamstown for Albany, leav- 

 ing the special geological study of the region in Dr. Dewey's 

 hands, and three years later he acknowledges (in his Index to the 

 Geology of the United States, 1820), "the assistance for two or 

 three years, of that very able and accurate naturalist, Professor 

 Dewey of Williams College," and shows his appreciation of the 

 knotty character of the region by the additional remark: "He 

 resides at the very central spot of the most complicated difficul- 

 ties, and never suffers any interesting fact to escape his notice." 



In January, 1819, Dr. Dewey was ready "with results, and 

 published, in the first volume of this Journal (p. 337-345), a geo- 

 logical description of the Williamstown portion of the Taconic 

 region. In 1820, in vol. ii of the same Journal (p.* 246), this 

 paper was followed by another on a " Geological section from the 

 Taconic Range in Williamstown to the city of Troy." By the 

 summer of 1824 he had much widened the range of his researches, 

 as shown in the eighth volume of this Journal (pp. 1 to 60 and 240 

 to 244), in an article the " Geology of Western Massachusetts 

 and a small part of the adjoining States," illustrated with a col- 

 ored geological map embracing all Berkshire, the southern por- 

 tion of Vermont, Canaan and Salisbury of Connecticut, and 

 eastern New York to the Hudson. 



The "Taconick Hills" first took their place in geological litera- 

 ture in his paper of 1819, in which (on p. 337) he mentions the 

 Indian orthography of Taconic and gave the word its present 

 shape. This first geological map of Berkshire, published in 1824, 

 shows the north and south direction of the belts of limestone ; the 

 Taconic backbone of the region, consisting, as he had found, of 

 " mica slate " and " argillite ;" the " primitive limestone " to the 

 east of the Taconic range, the " transition limestone," or less crys- 

 talline, to the west ; the isolated ridges of quartzyte, and areas 

 of mica schist and gneiss farther east ; the " gray wacke " and 

 slates farther west to the Hudson. Professor Dewey also ob- 

 served the general eastward dip of the rocks. Following Eaton, 

 he sought, by the terms " primitive," " transition," " gray-wacke," 

 to bring the facts into parallelism with those of English and 

 European geologists. Professor Dewey says, in his appendix to 

 this paper in the same volume (p. 242), "In Fishkill I found 

 petrifactions in siliceous slate associated with argillite.'''' This 

 very important discovery has not since been verified; but prob- 

 ably will be, since Lower Silurian fossils have been recently found 

 just north in the slate of Poughkeepsie, and many more in the 

 neighboring Barnegat limestone. 



It deserves mention that Dr. Dewey was enough of a chemist 

 to use the science to great advantage in his geological work. By 

 means of it he determined rightly the composition of the prevail- 

 ing slaty rock of the Taconic range, and set forth his determina- 

 tions repeatedly in his published papers. These slates were pro- 

 nounced by Eaton and others Talcose slates, because, like talc — 

 a magnesia mineral — they felt greasy. But in 1819 he said, " I 



