June 30, 1905.] 



SCIENCE. 



991 



these rocks could hardly be Cretacic, since the 

 fossils were of a more recent type. 



A careful study of the fossils has shown 

 that this material is not Cretacic but Eocene 

 in age. This fauna from Chappaquiddick 

 represents a new and distinct Eocene province, 

 differing from all the other Eocene provinces 

 of the Atlantic coast, but no more widely 

 different from these than they are from one 

 another. Although in this fauna there are 

 several species somewhat resembling those of 

 the provinces to the south, on the whole it 

 would seem to be more closely allied to the 

 Eocene of England. The genera most abun- 

 dantly represented in these Chappaquiddick 

 deposits, e. g., Modiola, Glycymeris, are also 

 among the most abundant in the English de- 

 posits. These same genera, although repre- 

 sented in the Atlantic and gulf provinces, are 

 there more sparsely distributed and occur with 

 other more abundantly represented genera 

 that appear to be altogether wanting in the 

 Chappaquiddick deposits. 



A comparison of this Chappaquiddick fauna 

 with other Eocene faunas indicates that it is 

 of lower Eocene age, the species most closely 

 resembling those found in this fauna being 

 found in the lower beds of the Atlantic and 

 gulf provinces, the Tejon of California and 

 the lower beds of England. These deposits 

 may possibly be of the same age as the Shark 

 River beds of New Jersey, but being deposited 

 in a region separated from this have no forms 

 in common with it. But such correlation 

 could be only conjecture. As the correlation 

 of the well-known Eocene deposits is even yet 

 very uncertain it is unnecessary and impossi- 

 ble to place these beds any more definitely than 

 simply to say that they are Lower Eocene. 

 Structural Relations and Origin of the Limo- 



nite Beds at Cornwall, N. Y.: C. A. Hart- 



NAGEL. 



The limonite at the Townsend iron mine, 

 near Cornwall in Orange County, N. Y., is 

 found at the base of the New Scotland beds 

 where the latter are in contact with the Long- 

 wood red shales. The source of the iron is 

 evidently from the red shales but whether the 

 contact was due to overlap or faulting has not 

 been previously explained. Two thirds of a 



mile north of the mine the Decker Ferry, 

 Cobleskill, Kondout, Manlius and Coeymans 

 formations, having a total thickness of 95 

 feet, are found between the New Scotland and 

 Longwood beds. In the region of the mine 

 the strata are nearly vertical and in faulting 

 a wedge-shaped block was forced up, bringing 

 the red shales in contact with the New Scot- 

 land beds. A cap of limestone has until re- 

 cent geologic times protected from erosion the 

 mass of soft Longwood shales which now form 

 a steep hill, but which is rapidly being worn 

 away. 



Types of Sedimentary Overlap: A. W. 

 Grabau. 



With a normal sea shore, a rising sea level 

 will produce the phenomenon of progressive 

 overlap, a falling sea level that of regressive 

 overlap. If the sea transgresses slowly, and 

 the rate of supply of detritus is uniform a 

 basal rudyte or arenyte is formed which rises 

 in the column as the sea advances, and whose 

 depositional off-shore equivalents are succes- 

 sive beds of lutytes or organic deposits (bio- 

 genics). Types of such basal beds which pass 

 diagonally across the time scale, are seen in 

 the basal Cambric arenytes of eastern North 

 America, which as the Vermont Quartzite are 

 lower Cambric, and as the Potsdam are Upper 

 Cambric. Again in the Basal Cretacic 

 arenyte of southwestern United States, this 

 is shown, these being basal Trinity in Texas, 

 Washita in Kansas, and Dakota or later on 

 the Front Range. Examples of this type of 

 progressive overlap are numerous and famil- 

 iar. On an ancient peneplain surface the 

 transgressing sea may spread a basal black 

 shale, as in the case of the Eureka (Noel) 

 Black shale, which is basal Choteau in south- 

 ern Missouri and basal Burlington in north- 

 ern Arkansas. Regressive movements of the 

 shore succeeded by transgressive movements 

 give us arenytes which are enclosed in off- 

 shore sediments and which within themselves 

 comprise an hiatus the magnitude of which 

 diminishes progressively away from the shore. 

 An example of this has recently been discussed 

 by Berkey * who finds that the St. Peter Sand- 

 stone in Minnesota marks the interval from 



* See ante, April meeting. 



