Geology and Mineralogy. 81 



liar ; of fourteen species of land shells, six are peculiar, etc. The 

 author gives an interesting summary of the conditions, as to 

 winds and ocean currents, which have been instrumental in the 

 introduction of the fauna and flora. 



2. On the Lower Silurian {Trenton) Fauna of Baffin Land y 

 by Charles Schuchert. Proc. U. S. Nat. Mus., vol. xxii, pp. 

 143-177 (with plates xii-xiv), 1900. — The author reports upon 

 several collections placed in his hands for study. The following 

 excellent summary is quoted from page 175 of the report: 



" The only Lower Silurian horizons known in northeastern 

 Arctic America are of Trenton and Utica age. The latter zone 

 appears only on the north shore of Frobisher Bay, but the Tren- 

 ton is found in various places from the north shore of Hudson 

 Strait to latitude 81° north. The Lower Silurian is thickest on 

 Akpatok Island, where it is from 400 to 500 feet in depth. Dr. 

 Bell, however, estimates the entire thickness of these strata in 

 this region to be not less than 900 feet. 



" In Baffin Land, and apparently elsewhere in Arctic America, 

 the Lower Silurian strata rests unconformably on old crystalline 

 rocks. To the north of Baffin Land, the former are overlain by 

 beds of Niagara or Wenlock age. 



" The Trenton faunas, occurring in various places around the 

 insular Archsean nucleus of North America, have much in com- 

 mon, and this indicates that the conditions at that time were very 

 similar, while the sea was in communication throughout. As 

 yet, however, the distribution of the strata, together with their 

 faunas, are well known only to the south and southeast of the 

 Archaean nucleus, yet that of the west (Manitoba) and of the 

 northeast (Baffin Land) show direct communication. 



" The Baffin Land fauna had an early introduction of Upper 

 Silurian genera in the corals Halysites, Lyellia, and Plasmopora. 

 In Manitoba similar conditions occur in the presence of Halysites, 

 Lavosites, and Liphyphyllum. Other Upper Silurian types do 

 not appear to be present. 



" The Trenton fauna of Silliman's Fossil Mount, at the head of 

 Frobisher Bay, has seventy-two species, of which twenty-eight 

 are restricted to it. This fauna shows an intimate relationship 

 with that of the Galena of Minnesota, Iowa and Wisconsin. 

 Fifty-seven per cent of the species of Baffin Land also occur in 

 the Galena of the regions just mentioned. 



"The Trenton fauna of Baffin Land shows that the corals, 

 brachiopods, gastropods, and trilobites have wide distribution, 

 and are therefore less sensitive to differing habitats apt to occur 

 in widely separated regions. On the other hand, the cephalopods, 

 and particularly the pelecypods, indicate a shorter geographical 

 range. The almost complete absence of Bryozoa in the Baffin 

 Land Trenton contrasts strongly with the great development of 

 these animals in Minnesota and elsewhere in the United States." 



3. A Preliminary Report on the Geology of Louisiana ; by 

 Gilbert D. Harris and A. C. Yeatch, Part V, Geology and 



Am. Jour. Sci.— Fourth Series, Vol IX, No. 55. — July, 1900. 

 6 



