556 



PROCEEDINGS OF THE ALBUQUERQUE MEETING 



d. The Lucas dolomite. — This name was proposed by Prosser in 1903 for 

 tlie upper dolomites so well exposed in Lucas county, Ohio. Here they mostly 

 rest directly on the Sylvania, the other beds being cut out by overlap. 

 The fauna is rich and peculiar, European types of gastropods predominating. 

 The genus Acanthonema Grabau, though represented in the Amherstburg, is 

 most characteristic, and the faunal zone may be designated the Acanthonema 

 zone. Its thickness varies up to 200 feet or over. Cijlindrohelium profundum 

 is restricted to it, and may be regarded as another good zone fossil. 



Pkoposed Classification 

 The proposed classification in tabular form is as follows: 



Upper Monroe f "^^ Lucas dolomUe (Prosser). (Zone of Cylindrohelium profundum and Acan- 



Detroit River Series j '^- Amherstburg dolomite (Sherzer and Grabau). (Zone of Panenka caim- 



7one of I ^- Anderdon limestone (Nattress). (Zone oi Idiostroma nattresii.) 



Prosserella. I "• ^'^' '""'^'^ (Lane, Prosser, Sherzer, and Grabau). Zone of Syringopora 



Disconformity. 



Middle Monroe Sylvania sandstone. 



Disconformity. 



Lower Monroe 



or 



Bass Islands Series 



(L., P., 8., and G.) 



Zone of 



Leperditia. 



d. Raisin river dolomite (Lane, Prosser, Sherzer, and Grabau). (Zone of 



Whitfieldella prosseri.) 

 c. Put-in-bay dolomite (Lane, Prosser, Sherzer, and Grabau). (Zone of 



Qoniophora dubia) 

 b. Tymochtee beds (N. H. Winchell). 

 a. Greenfield dolomite (Grubau). (Zone of Schuchertella hydraulica.) 



The papers were discussed by A. C. Lawson, A. P. Coleman, A. M. 

 Miller, H. M. Ami, I. C. White, and A. C. Lane. 



The concluding paper of the afternoon was 



STRUCTURE AND STRATIGRAPHY OF THE OUACHITA ORDOVICIAN AREA, 



ARKANSAS 



BY A. H. PUEDUE 



[Ahstractl 



The area herein considered lies in the western central part of Arkansas. It 

 is one of two Ordovician areas within the state, the other occurring in the 

 northern part and being the southern extension of the Cambro-Ordovician area 

 of Missouri. Between the two areas there is a large structural trough occu- 

 pied by rocks of Lower and Upper Carboniferous age, and containing the 

 Arkansas valley. 



The area is mountainous and is occupied by parallel east-west ridges. These 

 ridges have steep, rocky slopes and inclose narrow valleys. Many of them 

 reach from 1,800 to 2,000 feet above sea-level, or from 800 to 1,000 feet above 

 stream level. Through them occur numerous water-gaps formed by the south- 

 ward flowing streams. 



The general structure is that of an anticline with an east-west axis. This 



