378 ANNALS NEW YORK ACADEMY OF SCIENCES 



Francis M. Van Tiiyl and 



Fritz Berckhemmer, A IMioklematic Fossil fiiom the Cats- 



kill Formation. 



Francis M. Van Tuyl, 'I'm: Mottled Ti;ii;i:s 11 hi. Limestone 



and its Bearing on tiih Origin of 

 Dolomite^ 



A, W. Grabau, Tiik Black SiTale Puoblhm: a Study in 



Paleozoic Geography. 



'» 



Summary of Papers 



Dr. Berckhemmer sliowed bv meaii.'^ of lantern slides the presence of 

 the genus Sphwrocodiuni in Ordovicic rocks of this country, a matter of 

 unusual interest because it constitutes the earliest known occurrence of 

 this genus. A new species of calcareous algae from the Upper Ordovicic 

 was described, and pictures of the first known lime-precipitating algae 

 from the North American Siluric were exhibited. 



The paper was discussed by Dr. .'. M. Clarke and Dr. E. 0. Hovey. 



]\rr. Van Tuyl read his joint pa])ei- with Dr. Berckhemmer. He de- 

 scribed and discussed a fossil of uncertain affinities, collected from the 

 Catskill beds at Henrysville, Pennsylvania. The authors concluded that 

 the form could not safely be referred to any known groups of organisms. 



Dr. Clarke and Professor Grabau discussed the ])aper briefly. 



Mr. Van Tuyl, in his paper on limestone, showed that the mottled 

 structure of this limestone was due to the presence of irregular patches 

 of yellowish, coarse-grained dolomite, which stand oiit in relief on wea- 

 thered surfaces. The dolomitization proceeded either in an irregular 

 and imperfect manner by alteration along stratification lines or in dis- 

 connected patches; or in a more regular manner along definite lines 

 which appear to represent worm castings. In both types of alteration, 

 certain layers of the limestone have locally been completely changed to 

 <lolomite. It was concluded that the mettled limestone represented an 

 incomplete stage in the process of dolomitization, and that the alteration 

 had taken place at the time of, or very shortly after, deposition. 



The paper was discussed by Dr. Clarke and Professor Berkey. 



Di-. Grabau indicated, with the aid of maps and diagrams, jirobable 

 physiographic conditions which existed when the black shale was de- 

 posited. Various theories which have been proposed to explain this for- 

 mation were briefly outlined and criticized. The author concluded that 

 ihe shale represented fine black soil of a low-lying peneplain which was 

 in part washed into the sea by rivers, and in part reworked by waves and 

 currents as the sea transgressed the land. In the northern sections the 



