406 



SCIENCE. 



[N. S. Vol. XII. No. : 



notice of ' Piazzi Smyth,' by Kalph Copeland. 

 Notes as usual are published on variable stars, 

 planets and current spectroscopic work. 



DISCUSSION AND COBBESPONDENCE. 



NOTE ON THE SILUEO-DEVONIC BOUNDARY. 



In the recently published bulletin of the U. 

 S. Geological Survey, No. 165, entitled ' Con- 

 tributions to the Geology of Maine/ Professor 

 H. S. Williams has again defined his attitude 

 on the question of the Siluro-Devonic boundary 

 in America. Here the critical argument ad- 

 vanced with some emphasis for the construction 

 of the Helderbergian as a Siluric fauna is given 

 in the following words (p. 25) : 



"The boundary between the Silurian and Devonian 

 systems was first made in the Welsh series, in which 

 the transition was from calcareous sedimentation, 

 with rich and purely marine faunas, into sandstones 

 of great thickness containing land plants and fishes 

 whose habitat was, presumably, fresh or brackish 

 ■waters. 



" The New York section, from the Lower Helder- 

 berg limestones through the Oriskany, Cauda-galli, 

 and Schoharie grits back again into limestones, does 

 not pass out of marine conditions. In the Gasp6 

 region, however, there is a complete change (as there 

 was on the other side of the Atlantic Basin) at the 

 point where the Oriskany fauna was evolved. [Note 

 A.] In these Silurian faunas of the eastern province 

 there is also much closer resemblance to the Wen- 

 look-Ludlow series than is found in the faunas of the 

 Appalachian province in New York. The correlation 

 of the passage beds at the top of the Silurian of Wales 

 is clearly to be recognized in the passage from the 

 limestones to the Gaspe sandstones of the eastern 

 province of America. This Gaspe transition is also to 

 be traced with precision to the horizon of the intro- 

 duction of the Oriskany fauna into the basins farther 

 west and southwest, in which no direct passage into 

 Old Red sandstone condition is apparent. 



" We have thus in America a means of determin- 

 ing where the Silurian boundary belongs in purely 

 marine series of beds and among marine faunas of un- 

 broken succession. The Lower Helderberg in the in- 

 terior of the American continent, as the Koniprusien 

 F, fauna in the Bohemian Basin of Europe, is closely 

 related in its species to what succeeds, because there 

 was no radical disturbance of the conditions of marine 

 life. Nevertheless, it is not the Lower Helderberg 

 species that mark the conditions corresponding to the 

 beginning of the Old Red sandstone ; but the changes 



which that fauna suffered during the passage into the 

 Oriskany time are evidences of a general disturbance 

 which resulted in the lifting of large areas of marine 

 surface above the level of the sea. ' ' [Note B. ] 



Note A. — This statement is wholly inaccurate. 

 In the Gaspe limestones the Oriskany fauna 

 manifests itself pronouncedly with Hipparionyx 

 proximus, Rensselssria ovoides, Megalanteris, Ca- 

 marotachia pliopleura, Bhipdomella, cf. musculosa, 

 Meristella cf. lata, etc., at the base of Logan's 

 limestone No. 8, and above this horizon is the 

 great thickness of 500-600 feet of pure lime- 

 stone beds with chert bands, surprisingly sim- 

 ilar in lithologic aspect to the gray and choc- 

 olate-colored Onondaga limestones of New 

 York, and throughout these beds such Oris- 

 kany species are found in association with a 

 profusion of others not represented in the in- 

 terior basin Oriskany and many of them closely 

 comparable to species of the Helderbergian. 

 The plane of reappearance of certain Oriskany 

 species in the Gaspe sandstone above, was 

 shown by Logan to be 1100 feet above the top 

 of these limestones and to be restricted to a 

 comparatively slight vertical range. The fos- 

 sils of the sandstone are not abundant nor is 

 the fauna diversified. To any one studying 

 these relations on the ground it is clear that 

 they represent a brief return of the fauna of 

 the limestone with evidences of progression 

 and the further intermixture of species from 

 the interior province {Bensselseria cf. ovoides, 

 Chonostrophia daivaoni and Chonetes nielonica 

 (both of the latter in the New York Oriskany), 

 Lepiostrophia hlainvilli, cf. Oriskany species, 

 Orthothetes becraftensis, Phacops probably iden- 

 tical with P. anceps). The evidence from the 

 Gaspe series is potent and conclusive that the 

 introduction of the Oriskany fauna was accom- 

 panied by the deposition of pure calcareous 

 sediments which were continued for a pro- 

 tracted period and nearly equal in actual thick- 

 ness, the sum total of the Helderbergian and 

 Onondaga limestones in the New York area of 

 the interior basin. The species cited are in 

 themselves evidence of the wide transgression 

 during Oriskany time which is especially no- 

 ticeable in the distribution of the sediment in 

 New York. No tectonic change disturbs the 

 succession in the 2000 feet of Gaspe limestones. 



