266 CALCIFEROUS SANDSTONE. 



The most important of all these fossils, are the two genera of trilobites, Conoceplialites and Dikelocepha- 

 lus, because in Bohemia, England and Spain, these forms of life are found in the very oldest fossiliferous 

 strata. In Bohemia the strata are said to belong to the " Primordial Zone of Life ;" and in England, by 

 the Government Geologists, to the " Lingula Flags." It seems then the opinion, expressed by eminent 

 naturalists in this country years ago, is confirmed by the recent discovery of these trilobites, viz : that in 

 the Potsdam sandstone are found the remains of the oldest inhabitants of North America. It is certainly 

 very singular, that in the lithological character and thickness of the strata, there should exist such great 

 differences upon the two sides of the Atlantic Ocean. There are, however, series of strata in Eastern 

 Massachusetts and elsewhere on the coast, containing the Paradoxides Harlani, another characteristic fossil 

 of the primordial zone of life, which agree more nearly with the European groups. And there is a very 

 warm discussion being carried on at this time respecting the age of certain rocks in Vermont, which are 

 referred to the primordial zone of life by eminent authorities. In another part of this Eeport both parties 

 in this discussion speak for themselves. 



Some geologists have considered the JScolithus linearis as a characteristic fossil of the Potsdam sandstone, 

 and have pronounced certain belts of rock to be of this age from its presence in them. This fossil is found 

 in great abundance in Vermont, in the quartz rock at the western base of the Green Mountain range. If 

 the early opinion of the Scolithus is correct, then the determination of the age of the quartz rock would be 

 easy. But for various reasons, which are stated elsewhere, we do not regard this fossil as necessarily 

 characteristic of the Potsdam sandstone. 



CALCIFEROUS SANDKOCK. 



This is the second rock overlying the Laurentian series, and there is considerable thick- 

 ness and extent of it in Vermont. 



Lithological Characters. 



The prevailing character of this rock is that of a sandy limestone, compact and thick- 

 bedded. There are several varieties, which we will mention in no determinate orders, as 

 we have measured no careful section of this formation. 



1. THE COMMON SANDY LIMESTONE. 



2. GEODIKEROUS STRATA. 



3. LIGHT COLORED LIMESTONE. 



4. BRECCIATED LIMESTONE. 



5. PURE QUARTZ SANDSTONE. 



6. CLAY SLATE. 



7. FUCOIDAL LAYER. 



The first variety is very common. Most of the specimens are of this description for 

 example, Nos. r ^, ^5 to j^, etc. This rock forms the transition from pure sand- 

 stone to pure limestone, and therefore partakes of the character of each. Generally the 

 sand predominates. Very frequently these strata contain geodic masses of quartz and 

 calcite, and also chert. These form the second variety. They invariably give off a fetid 

 smell when broken. Wherever the first variety occurs the second generally accompanies 

 it. Occasionally small masses of bituminous matter fill little seams and cavities of 

 this rock, and in some cases where it is disseminated in minute particles it imparts a dark 

 color to it. The geodic quartz and calcite, though generally white, are sometimes 

 black, as in No. ^. ' Some of these varieties have a red surface, as in No. j^, where 

 it is very bright, and may perhaps result from small ferruginous concretions resembling 

 fucoids. 



