424 J. D. Dana — Brief history of Taconio ideas. 



began his numerous discoveries of Trenton and Calciferous 

 fossils in the belts of " Sparry limestone " of Dutchess Co., 

 !N. T., which he has continued to 1888;* and in 1885 and 

 1886 made other discoveries in the " Sparry limestone " — 

 strictly the southern part of the Eolian — in Canaan, Columbia 

 Co., 'N. Y., just west of the Taconic Range.f Thus the evi- 

 dence of the Lower Silurian age of the limestone and slate went 

 on accumulating. Further, both Hudson River and pre-Pots- 

 dam Cambrian fossils were reported by Mr. S. W. Ford from 

 the east border of the Hudson near Schodack landing,^ and 

 Upper Cambrian by Professor Dwight near Poughkeepsie,§ 

 both being cases of the uplift of Cambrian beds along a fault.- 

 Professor Dwight found the Hudson shales to be the prevail- 

 ing rock in Dutchess County; also that it was intersected by 

 numerous faults : Potsdam occurring faulted against Trenton, 

 against Calciferous and against Hudson shales ; and the Cal- 

 ciferous against Trenton and Hudson shales. Again, in 1886,- 

 Mr. I. P. Bishop, of Chatham, Columbia Co., 1ST. Y., eight 

 miles southwest of Canaan, announced| the occurrence of 

 Hudson group graptolitic schists' and fossiliferous Trenton 

 limestone at that place, and the continuation of the beds north- 

 ward to the borders of Rensselaer Co., 1ST. Y., and south to 

 Ghent — facts that bore on the age of the " Taconic slate " of 

 Emmons not only for Columbia County but also for the region 

 north. 



My papers appeared in this Journal in 1872, 1873, 1877, 

 1879, 1880, 1884, and finally in 1885 and 1886, the series was 

 continued, with new results, and the completion of a geological 

 map of the limestone areas of the Taconic region east and 

 west of the Taconic Range from Northern Bennington in 

 Vermont to the southern limit of Canaan and Salisbury, Conn. 

 It is not necessary to mention here conclusions. I was slow in 

 reaching any positive conclusion about the age of the quartzyte 

 because of the non-discovery of fossils, which I made the only 

 reliable evidence of age. But in 1884 discovering chondro* 

 ditic limestone in eastern Berkshire as evidence of the presence 

 of Archsean, I made out an eastern quartzyte as Potsdam or Cam- 

 brian, leaving the quartzyte that alternates with the schists 

 and limestone in the center of the Taconic limestone region, 

 still in doubt. But the evidence was not sufficient to prove 

 that there was a continuous belt of Archaean along eastern 

 Berkshire and the Green Mountain Range to the north, so that 



* W. B. Dwight, this J., Ill, xvii, 389, 1879, xix, 50, 451, 1880, xxi, 78, 1881, 

 xxvii, 249, 1884. 



f W. B. Dwight, this J., xxxi, 248, 1886. 



IS. W. Ford, this J., Ill, xxviii, 35, 206, 242, 1884, xxix, 16, 1885. 

 § W. B. Dwight, this J., Ill, xxxi, 125, 1886, xxxiv, 27, 1887. 

 || I P. Bishop, this J., xxxii, 438, 1886. 



