GEOKGIA GEOUP. 357 



Scolithus appears more distinct than usual. Beautiful specimens of the Scolithus in this decomposed 

 rock occur at Harwood's Quarry. We have also seen much of this fossil in Sunderland, upon the route 

 of Section III, (No. &, in the Cahinet.) 



Many have considered this fossil as characteristic of the Potsdam sandstone. If this be so, then the age 

 of the quartz rock is certainly known. It certainly has never been described from any other rock; but we 

 do not feel authorized to accept the positiveness of its evidence, because (1) of its anomalous character; 

 and (2) because it is found in a metamorphic rock, and may, therefore, have been altered from some species 

 of organism, considerably different from the original of the Scolithus. For instance, upon the supposi- 

 tion that the quartz rock is middle silurian, we should imagine the Fucoides verticalis of the Oneida 

 conglomerate would change into a form, not distinguishable from the Scolitlius linearis. 



We collected no specimens of the fucoids, which are quite common at the "upper bridge" in Bristol, 

 though quite obscure. In the southwest part of Woodford, there seem to be traces of organism, resembling 

 bivalve shells, about the size of a three cent piece. They are too obscure for recognition. 



GEORGIA GROUP. 



PRIMITIVE ARGILLACEOUS SLATE: Prof. Chester Dewey's Geological map of Berkshire, 

 Mass.; Columbia and Rensselaer Counties, N. Y.; American Journal of Science and Arts, 

 I. Series, Vol. VIII ; 1824. 



PRIMITIVE ARGILLACEOUS SLATE : Geological Report of Massachusetts, 1832. 



BLACK SLATE AND TACONIC SLATE. ROOFING SLATE OF THE UPPER PART OF THE 

 TACONIC SYSTEM : Prof. E. Emmons' works on the Taconic System, 1840 1860. 



HUDSON RIVER GROUP OR LORRAINE SHALES : Geological map of New York, 1842 ; 

 also in the Palaeontology of New York, Vol. I ; by Prof. James Hall; 1847. 



" ROOFING SLATE OF THE TACONIC SYSTEM;" but considered as of the Hudson River 

 Group : Reports on the Geology of Vermont, 1845 1847 ; by Prof. C. B. Adams. 



TIPPER PART OF THE HUDSON RlVER GROUP, OR A DISTINCT GROUP ABOVE THE 



HUDSON RIVER GROUP : Quoted by Prof. James Hall, from the opinions of Sir William 

 E. Logan ; Twelfth Annual Report of the Regents of the University of the State of New 

 York; 1859. 



UPPER HUDSON RIVER GROUP : Elementary Geology, 31s edition, p. 411 ; by Edward 

 Hitchcock, and C. H. Hitchcock ; 1860. 



SLATES CONTAINING THE FIRST FAUNA, OR THE PRIMORDIAL ZONE OF LIFE : Letter 

 from M. Joachim Barrande to Prof. Bronn, of Heidelberg, July 16, 1860. 



BELONGING TO THE PRIMORDIAL ZONE OF LIFE, AND PERHAPS THE EQUIVALENT OF THE 

 POTSDAM SANDSTONE : Letter from Sir Wm. E. Logan to M. Joachim Barrande, Jan. 3, 1861. 



The rocks included under this head are distributed in two (perhaps three) terrains in 

 Vermont, which are identified by their organic remains, viz., Barrandia Thompsoni 

 (Hall), etc. The most northern terrain is found in Franklin and Chittenden Counties, 

 extending probably from Quebec. The second terrain is seen first in Cornwall, in 

 Addison County. From thence it gradually enlarges, and is several miles wide as it 

 leaves Rutland County, and passes into New York. The third terrain, in which no 

 fossils have been found, and is therefore not certainly of this age, is a band of clay slate, 



