January 19, 1900.] 



SCIENCE. 



105 



boundary between the two systems, Silurian 

 and Devonian, the standard sections of 

 which are on another continent, and (6) of 

 the facts of correlation bearing upon the 

 case. 



He urged that to establish the top of the 

 Silurian as the word was used by Murchison, 

 we must find the equivalent of the Tilestone 

 fauna. This has been done in the Arisaig 

 fauna of the Maritime provinces, which is 

 well developed in northern Maine and 

 which lies over the Helderberg fauna at 

 the same place. He therefore developed 

 an argument for retaining the Helderberg 

 in the Silurian. 



The contact of the Silurian and Devonian in 

 Erie Co., N. Y. By A. W. Geabatj, Troy, 



]sr. Y. 



A limestone known as the Bullhead 

 rock was found to contain fossils like those 

 described by Whitfield from the Helderberg 

 of Ohio. There is an unconformity between 

 the Bullhead rock and the overlying Onon- 

 daga. A sandstone dike in a crevice in the 

 limestone was described and some sugges- 

 tions regarding the choice of a name for the 

 Bullhead rock were made. The Manlius 

 limestone was finally adopted, it having 

 been used by Dr. J. M. Clarke. 



Devonian strata in Colorado. By Arthur C. 



Spencer, Washington, D. C. 



The presence of Devonian rocks in south- 

 western Colorado, asserted by F. M. End- 

 lich in 1874, has been confirmed by obser- 

 vation of the United States Geological 

 Survey party under the direction of Dr. 

 Whitman Cross. 



The section when complete is threefold, 

 consisting of a conglomerate and sandstone 

 at the base, followed by a calcareous shale, 

 and this by a massive limestone containing 

 considerable numbers of invertebrate fossils. 

 The limestone is shown by its outcrops to 

 have covered an area of at least 600 square 

 miles. The sandstone and shale beds are 



locally absent through non-deposition. 

 Their age is possibly Silurian, though they 

 contain occasional fish remains, which 

 would ordinarily be considered indicative 

 of the Devonian. The silicious series is 

 correlated with the ' Parting Quartzite ' of 

 central Colorado, and mention is made of 

 further probable equivalency between this 

 series and the supposed Devonian of the 

 Grand Canyon region. This brings out the 

 probability that these formations of the 

 Middle Paleozoic were originally deposited 

 over a very extensive area in the southern 

 Rocky Mountain region. 



The fossils have been studied by Dr. 

 George H. Girty, who considers that they 

 are representative of a fauna older than 

 that of the Chemung, and probably belong- 

 ing at the base of the upper Devonian or 

 near the top of the lower. Collections 

 made by various geologists in central Colo- 

 rado, are found to contain the same assem- 

 blage of fossils and to afford a basis for corre- 

 lation. The fauna resembles that described 

 by Whiteaves, from Hay River, Canada. 



All four Devonian papers were discussed 

 together. J. M. Clarke urged, regarding 

 the delimitation of the Silurian, that it 

 should rest upon the organic forms and 

 their culmination, and not on the classifica- 

 tion of Murchison. He then emphasized 

 the Devonian aspects of the Helderberg of 

 New York most strongly, and stated that 

 its rich fauna should decide the question 

 and with it the Arisaig would go. Dr. 

 Clarke also corroborated the observations 

 of Grabau by his own studies in the cement 

 quarries of Buffalo. 



H. S. Williams stated his method of 

 solving the Devonian question as an en- 

 deavor to find in America an equivalent 

 section to the classic section of the Old 

 World. He therefore had searched for it 

 in Maine and had discovered one above 

 the Helderberg, which was almost exactly 

 equivalent to the Tilestone. Other con- 



