ORDOVICIAN FAUNAS IN LAKE CHAMPLAIN VALLEY 459 



As this is the most northerly locality of the Trenton which we have so far observed 

 within the Champlain valley, it is interesting to note that several of the same zones 

 found in the extreme southern section at Larrabee point persist, although the ap- 

 parent thickness of the layers is a great deal less than at points farther south, per- 

 haps largely in consequence of squeezing and forcing of the layers out of their true 

 position, as the result of the crumpling of the anticline. 



On the opposite side of the lake at Rouse point, at Point- au-Fer, and on Alberg 

 peninsula, the Utica formation occurs, in vafious outcrops, but containing few 

 fossils. 



Range of particular Faunas and Species 



The Black River formation is characterized in the region, in its lower portion, 

 by a zone composed almost exclusively of LeperdUia fabulites, best shown on Button 

 island, but also seen elsewhere. 



The next well marked zone is that of Stromatocerium rugosum, Columnaria alveo- 

 lata, Tetradium fihratum, and Rhynchotrema inxquivalve, which extends through over 

 60 feet of the top of the Black River, and with which fossils are associated Stro- 

 phomena billingsi and ^S". incurvata, Zygospira recurvirostris, and Z. exigua, Zaphrentis 

 canadensis, Schizocriyius nodosus, Bumaslus trentonensis, and Thaleops, probably ovata. 



Near the top of the Black River, in a zone particularly well marked at Chazy, 

 New York, is a large species of Maclurea, which both in stratigraphic position and 

 in specific characters is distinct from Maclurea magna of the Chazy. which occurs 

 so abundantly in the neighborhood. It is a large species, more rounded than 

 M. magna, and marked with concentric grooves around the periphery, and is prob- 

 ably identical with M. logani of Canada. Its associates ave Stromatocerium rugosum, 

 Rafinesquina alternnta, Rhynchotrema, insequivalve, Dalmanella testudinaria, Hormatoma 

 gracilis, Lophospira hicincta, Lingida elongata, Calymmene senaria, Ceraurus pleurex- 

 anthemus, etcetera. 

 . Dalmanella testudinaria, Rafinesquina alternata, Plectamhoniles sericeus, Protowarthia 

 cancellata, Calymmene senaria, Ceraurus pleurexanthemus, and Trinucleus concentricus 

 are found universally through all the beds of lake Champlain valley. 



Doctor Sardeson has recently attempted* to correlate by the employment of spe- 

 cific or varietal names the forms of Plectambonites sericeus and' Dalmanella testudinaria 

 of Minnesota, and a suite of the representatives of those species from our localities 

 was sent him. He determines among them the varieties P. sericeus aspera James, 

 a form related to P. minnesotensis Sardeson, P. recedens Sardeson, and Dalmanella 

 testudinaria meelci Miller, D. emacerata Hall, a form related to D. porrecta Sardeson 

 and D. suhiequata var. gibbosos of Billings. A tabulation of the occurrences of these 

 forms, as identified in the lake Champlain valley, does not indicate any rule of 

 variation of one to another, but all appear to be irregularly distributed througli 

 the series, the variation being due more to changes in the character of the deposits 

 and life conditions in particular beds than to any progressive order of evolution to 

 established fixed types. 



A short distance above the top of the Black River occurs a zone which may be 

 traced the whole length of the lake by its abundance of Parasirophia hemipMcata. 

 This fossil occurs scatteringly higher in the series, but is nowhere else abundant, 

 and it appears in force without precursors below. The younger specimens very 



* F. W. Sardeson : American Geologist, vol. xix, 1897, pp. 91-111 and 180-190. 



