the Horton-Windsor District, N. S. 165 



environmental conditions. There are three and probably 

 four zones of calcium sulphate deposits (gypsum and an- 

 hydrite), averaging roughly 50 feet each, separated by 

 varying amounts of brick-red argillaceous shale and fos- 

 siliferous limestone with subordinate thin dolomitic 

 sandy shales, oolites, and calcareous algal bands. In 

 amount, the gypsum and anhydrite may make up some 10 

 per cent of the total estimated thickness of 1100 feet, with 

 red shale 50 per cent and calcareous beds 40 per cent. 

 Estimates of the thicknesses of this series, however, must 

 be considered as but very rough approximations, owing 

 to the poorness and isolated nature of the exposures, and 

 to the presence of numerous fault slips of which mention 

 has been made. The sequence of faunal zones presented 

 here is necessarily dependent on the writer's interpreta- 

 tion of the structure, and is not advanced as an estab- 

 lished fact. Better and less broken sections may be found 

 elsewhere in the province that will necessitate a consider- 

 able revision of the following succession. The sequence 

 as given below is radically different from that presented 

 by Hartt (1867) and in Dawson's ^^Acadian Geology.'' 



Upper Windsor or Martinia zone. Characterized by 



Martinia opertacosta n. sp. 

 Subzone D. Characterized by Caninia dawsoni (Lambe) 460'± 

 Subzone C. Characterized by Didunophyllum lamhei n. 



sp 270' 



Lower Windsor or Composita zone. Characterized by 



Composita dawsoni (Hall & Clarke). 

 Subzone B. Characterized by Diodoceras avonense 



(Dawson) 265'± 



Subzone A. Basal limestone and Sanguinolites phase. . 95'zb 



The Windsor beds disconformably overlie the Cheverie 

 formation. The basal member is a fine calcareous quartz- 

 ite whose upper surface is locally marked by interior 

 molds of the valves of a Sanguinolites. Commonly both 

 valves are attached and flatly opened. A thin conglom- 

 eratic development with limestone pebbles, probably of an 

 intraformational character, follows the basal arenaceous 

 bed, and is succeeded by platy brecciated limestone which 

 carries calcite vugs and occasional nodules of pyrolusite 

 and manganite of secondary origin. This manganif erous 

 mineralization is of such widespread occurrence at this 

 horizon that it is probable that the manganese content 

 was originally disseminated in the limestone at the time 



