54 



THICKNESS OF STRATA. 



case in the fossiliferous rocks below the carboniferous, because these embrace nearly all 

 the fossiliferous rocks in Vermont. Below will be found these formations, with their 

 European and American divisions and thickness in feet, measured on a line perpendicular to 

 the planes of stratification. The subdivisions are those employed in the geological survey 

 of New York, because they have got into more general use than those more recently pro- 

 posed by Prof. Henry D. Rogers. 



Formations. 



DEVONIAN. 



UPPEK SILURIAN. 



European Divisions. 

 { Upper, 



Middle, 



Lower, 



Tilestone, 



Upper Ludlow Rock, 

 Ayrnestry Limestone, 

 Lower Ludlow Rock, 

 Wenlock Limestone, 

 Wenlock Shale, 

 Woolhope Limestone, 

 Denbighshire Sandstone, 

 Tarannon Shales, 

 May Hill Group, 



Thickness. 



10,000 



N. American Divisions. Thickness. 



' Catskill Red Sandstone, 5000 



Cheinung Group, 3200 



Portage Group, 1700 



Genesee Slate, 300 



Hamilton Group, 600 



Marcellus Shales, 300 

 Upper Helderberg Limestone, 350 



Schoharie Grit, ) o 

 Cock-tail Grit, \ 



Oriskany Sandstone, 200 



11,950 



f Lower Llandovery Beds, 

 ,T. a** Caradoc Sandstone, 



LOWER SILURIAN. < T , -i 171 



Llandeilo Flags, 

 [ Lingula Flags, 



800 



650 



100 



1000 



300 



1500 



50 



2000 

 1000 

 1000 



8400 



1000 

 9000 

 5000 

 5000 



20,000 



f Lower Helderberg Limestone, 

 Water Lime Group, ) 

 Onondaga Salt Group, > 

 Niagara Group, j 



Clinton Group, 

 Medina Sandstone, ) 

 Oneida Conglomerate, \ 



Hudson River Group, 

 Utica Slate, 

 Trenton Limestone, 

 Chazy Limestone, 

 Calciferous Sandrock, 

 Potsdam Sandstone, 



300 

 1000 



2400 

 1450 



6150 



2000 



500 



2500 



2500 



100 



300 



5900 



CAMBRIAN. Cambrian, 26,000 Huronian, 12,000 



Azoic. Hypozoic, Laurentian, 20,000 



Some geologists describe rocks in a descending and some in an ascending order. Pecul- 

 iar circumstances lead us to deviate somewhat from either of these modes. We propose, 

 merely for convenience and not for the sake of scientific classification, to describe the 

 rocks of Vermont in the four following groups : 



1. ALLUVIAL AND TERTIARY ROCKS. 



2. HYPOZOIC OR LAURENTIAN AND PALEOZOIC ROCKS. 



3. Azoic ROCKS. 



4. UNSTRATIFIED ROCKS. 



