R.WMON'i) : The Cha/v I'ormatiox and its Fauna. 549 



and range of species. It will be noted that the divisions made on 

 purely faunal grounds correspond cpiite closely to their divisions, 

 although the limits of the divisions are somewhat different, es])ecially 

 at Chazy and Crown Point. 



As a definite horizon marker, Macliirifcs i/iag/ius can not be de- 

 pended upon, as it ranges all through the section. In a general way, 

 however, when abundant, it is an indicator of a middle Chazy horizon, 

 and if accom])anied by /\aJi/u-S(/i///ia chaiiiplaincnsis, Phesioiiiys platys, 

 CiDucrella varians and Lcperditia liniattda, the fauna may be known 

 as of middle Chazy age, whatever its position in the section under con- 

 sideration. 



Faiimilcs in the Typical CJiazy. 



There are certain faunules which can be readily recognized in the 

 typical Chazy deposits of the Champlain A'alley. These are: 



First. The Lingi/Ia l>raincrdi faunule. This faunule is found in 

 the basal sandstones and shales of the Chazy formation at Crown Point, 

 Valcour Island, Isle La Motte and South Hero, and thus marks the 

 base of the sections throughout the region of Lake Champlain. Fre- 

 quently Lingula hrainerdi is the only fossil present other than the 

 fucoidal markings, but at Valcour Island the faunule consists of the 

 following species : 



Lingula hrainerdi, Oriiioeeras sp. ind., 



Eccylioptenis ? sp. , Isoteliis harrisi. 



This faunule ranges through only about ten to fifteen feet of rock, 

 and is not a horizon marker, but merely indicates the base of the in- 

 dividual section. 



Second. The Scalites angulatus faunule. This faunule has been 

 found in only three localites ; one of them just north of the Normal 

 School at Plattsburgh, N. Y., and the other two at Chazy. It ranges 

 through only a few feet of strata. Its position in the section is know'n 

 only at Chazy, where it is 500 feet below the top. It has not been 

 found on Valcour Island, the strata in which it might be e.xpected to 

 occur being absent from the section on the south end of the Island, 

 where, at Pebble Beach, over a hundred feet of the lower layers are 

 missing. 



The composition of this faunile is not exactly the same at Chazy 

 and Plattsbursrh, as is shown in the following lists : 



