OF ARTS AND SCIENCES. 219 



Bat. ohlongus^ Bat. copax ; Arionellas ; Amphion Salteri; Cheirurus, 

 Asaphics, lUcenas ; Lituites Farnsworthi, Lit. imperator ; Orthoceras 

 Marcoiu'., Orth. llissisqnoi ; Nautilus Pomponius ; Maclurea mutu- 

 titia, Mad. ponderosa ; Ecculiomphalus canadensis, Ecc. intortus, Ecc. 

 spiralis; Metoptoma Niobe, Met. Orlthya., Met. ILjrle., Met. Augusta; 

 Murchlsunla Vesta ; Pleurotomaria posluma ; Camerella calclfera ; 

 Leptcena sordlda, Lep. decipiens ; Orthis gemmicida, Ort. Tritonia ; 

 Ort. Electro^ Ort. Hippolyte, Ort. Endosia ; and StricMandla ? Arachne, 

 Acrotreta, Obolella, antl Lingula. 



4th. Swanton slates formed of black slates inter.stratified now and 

 then with thin hiyers of a marly limestone ; they are about twenty-five 

 hundred feet thick. A few lenticular masses of limestone are enclosed, 

 containing at Highgate Springs and some other places colonies of the 

 second fauna, with Trinuclens concentrlcus ; Cahjmene Blumenhachii ; 

 Ampyx Hall I ; Orthis Ignx ; Rliynchonella increhescens ; Stenopora 

 fibrosa, Sten. PetropoUtana ; Ortlioceras, Murchisonia, Columnaria, 

 and Lingula. 



The Graptolite beds so numerous near Point Levis and at Swan- 

 ton Falls are in this group. 



A dislocation of great magnitude occurred at the end of the deposit 

 of the " Swanton slates." 



5th. Potsdam sandstone, with its well-known rocks, lies in discord- 

 ance of stratification over these different groups, and is found in many 

 places where it has not been entirely destroyed and washed away by 

 erosion. At Lake Champlain the Potsdam has been much eroded, 

 and we have only the lowest part of it, about three hundred feet thick. 

 The fossils are: Conoceph(dites Adamsi, Con. Vulcanus, Con. minutus, 

 Con. verrucosus; Lingidepis minima, and Obolella prima. 



Another dislocation occurred at the end of the deposit of the Potsdam, 

 but not so important as the preceding one of the " Swanton slates." 



Champlaix Series or Group. — Just alongside, not more than 

 half a mile distant from this typical region of the " Taconic system " 

 of the eastern shore of Lake Champlain, are the peninsula of Alburgh, 

 the Isle la Motte, and Chazy Landing, forming Emmons's group of 

 Lake Champlain, with all its rocks and characteristic fossils, so totally 

 distinct from the Taconic system. The Cliamplain group rests in dis- 

 cordant stratification of about 15^ or \Cp upon the Potsdam sandstone, 

 very near the village of Chazy, and also at one mile to the west of the 

 village. 



The Cakifcrous sandroch, ."GO feet thick, contains Maclurea matu- 

 tina, Turbo obscura, and Orthoceras jnimigenium. 



