666 



REPORT OF NATIONAL MPSEUM, 1904. 



In 1849 the ubiquitous Hunt entered the Held, siding, as il chanced, 

 with the opinions of the opponents of the system, though later lie 

 shifted his ground. No new facts were, however, presented, and the 

 matter is mentioned here only on account of the characteristically 

 emphatic and apparently decisive manner in which his opinions were 

 expressed, however fanciful may have been their basis. 



Little of consequence now occurred until L855, when Professor 

 Emmons brought out his volume on American Geology, in which he 

 made his third presentation on the subject. In this he extended the 

 system from Maine to Georgia and subdivided it into an upper and 

 lower portion, the fossiliferous portion being called the Upper Taconic 

 and the nonfossiliferous the Lower Taconic. The Sparry and Stock- 

 bridge limestones were brought together as one formation, while the 

 s3 T nclinal character of Mount Greylock was recognized and figured. 



Upper Taconic 



Lower Taeoni< 



Taconic system in 1855. 



2. Black slate of Bald Mountain. 



1. Taconic slate. 



3. Magnesia slate. 



2. Stockbridge limestone. 

 1 . Granular quartz. 



As here given, the system, as stated by Dana with reference to that 

 ot 1844, had a top and bottom of Cambrian rocks. The succession in the 



Lower Taconic was the same as 

 in the publication of 1844. 



In 1854 or 1855 trilobites re- 

 lated to those of Bald Moun- 

 tain were found in the Black 

 slates of West Georgia, Ver- 

 mont. Passing into the hands 

 of Zadock Thompson, the as- 

 sistant in the geological survey 

 of the State, the specimens 

 were sent to Professor Hall, 

 and in 185!> were figured and described as belonging to the shales of 

 the Hudson River group, one of the minor subdivisions of the Lower 

 Silurian system, under the names of Olenus thompsoni, 0. vermontana, 

 and Peltura holopyga, the beds being thus, in his opinion, made equiv- 

 alent to the Bald Mountain slates already noted. In this he was, how- 

 ever, in error. 



The problem was not, how T ever, confined to American soil. In L856 

 there were found in the limestone belonging to the so-called graywacke 

 series at Point Levi, opposite Quebec, a trilobite fauna of a nature 

 sufficient to convert the paleontologist, Elkanah Billings, of the Cana- 

 dian survey, to the views of Emmons, and cause him to affirm that the 



a b 



Fig. 135.— a, Triarthus beckii; h, Triarthus eatcmi. 



