244 



Potsdam Sandstone. — In Vermont the Potsdam Sandstone has ex- 

 actly the same aspect and composition as at Potsdam, in the State of 

 New York. Near Saxe's Mills, a mile east of the Highgate- Springs, 

 it contains two species of ConocepliaUtes, C. Adamsi and C Vulcanus. 

 Being the capping group of the Taconic in the renversnnent (overturn) 

 of the strata, it has been broken into pieces and narrow parallel 

 bands, which have rested upon the more inclined strata in a sort 

 of unconformable stratification, very apparent everywhere, squeezing 

 the Lingula-flags and Georgia Slates near the point of contact, and 

 giving them for about two feet depth a sort of agitated structure 

 (structure tourmentee). These narrow bands of Potsdam Sandstone 

 are numerous and well developed west of Mr. Parker's farm at Georgia, 

 and also on the road between St Albans and S wanton ; at first they 

 appear to be interstratified with the Georgia Slates, but they are not 

 so, and may be compared to the steps of a ladder placed over, or 

 even a little wedged into the Georgia Slates and Lingula-flags. This 

 group has been known for a long time in Vermont by the name of 

 Red Sandrock. It is found all the way from Saxe's Mills to Western 

 Georgia. It forms the top and eastern side of Snake Mountain, con- 

 trary to the view of Dr. Emmons, who refers these Snake Mountain 

 rocks to the Calciferous Sandstone. All the fossils found until now in 

 the Potsdam Sandstone of Vermont and New York are of primordial 

 form ; and there is also a great break and discordance of stratification 

 between this group and the Lower Silurian ; and I think the opin- 

 ion I first expressed one year ago is fully justified by paleontological 

 and stratigraphical evidences. 



Below the Potsdam Sandstone lie great masses of slates, four or five 

 thousand feet thick, which for convenience I should divide into three 

 parts. No regular line of division can be traced between these three 

 groups, as the strata pass from one to the other without any well 

 marked difierence ; it is merely for the fossils, and as a matter of con- 

 venience, that I propose the division. 



Lingula-Jiags. — The upper group, or Lingula-flags, is formed of 

 brown, green, and blackish slates, five or six hundred feet thick, with 

 numerous lines of cleavage, cutting the strata in all sorts of direc- 

 tions. In some parts the fossils are very numerous, and I found at 

 Highgate- Springs, where I first saw them, in company with Dr. Hall, a 

 quantity of Lingulce, OrtJiis, Orlhisina, and Chrondites. The Lingula 

 is new, and the Orlhisina is nearly related to, if not identical with, 

 an Orlhisina quite common in the Lingula-flags of Wales in Great 

 Britain. Mr. Billings informs me that since my visit there he found at 

 Phillipsburgh some Graptolites, in slates near the shore of the lake, 

 which I consider as of the upper group, or Lingula-flags. 



Georgia Slates. — The middle group, or Georgia Slates, is composed 



