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group, the lowest of the Carboniferous horizons or, possibly, 

 belonging to the Devonian in part or in whole. 



As a result of recent investigations in the Sydney field, 

 Hyde (see later pages) divides the original Limestone 

 series in two and links the upper subdivision with the Mill- 

 stone Grit, and the lower with the typical Windsor series. 



The geological structure of the Sydney Carboniferous 

 area is of a comparatively simple type. Over large areas 

 the strata dip with low angles ranging in value from 5° to 

 20°, and the greater part of the district is free from faulting. 

 The whole basin is divisible into four subordinate synclinal 

 basins whose axes in the west, strike N.E. and S.W. but 

 towards the east have a more nearly E.-W. trend. These 

 folds with their limbs in most cases dipping at low angles, 

 apparently all pitch seaward so that along the coast, the 

 highest Carboniferous strata, the Productive Coal Measures, 

 form, save for blank spaces due to indentations of the sea, 

 a nearly continuous band striking northwesterly at right 

 angles to the courses of the axes of folding. 



On the western side of the field, the basin is bounded by 

 the bold range of the St. Anne hills composed of Pre- 

 Cambrian and Cambrian strata rising to heights of from 

 500 to 1,000 feet (150 to 300 m.). In places the hills rise 

 directly from the shore of the Great Bras d'Or channel; in 

 other places they are separated from the waters by a narrow 

 fringe of the Limestone series; while, towards the north- 

 east, they are divided by a pronounced fault from a small 

 basin of the Productive Coal Measures and older divisions of 

 the Carboniferous. 



Separated from the St. Anne range by the Great Bras 

 d'Or channel, lies Boularderie island, about 25 miles 

 (40 km.) long, and representing a synclinal basin mainly of 

 Millstone Grit, this being the most westerly of the four 

 synclinal basins of the field. To the southeast of the island 

 and separated from it by St. Andrew channel, rise the 

 Boisdale hills composed of Pre-Cambrian and Cambrian 

 strata. This range extends in a S.W.-N.E. direction and 

 represents the axial portion of an anticlinal that strikes 

 through the northeastern extremity of Boularderie island. 

 The Boisdale hills are in part flanked by strata of the 

 Conglomerate series but in places members of the Limestone 

 series repose directly on the ancient strata of the range of 

 hills. A seeming overlap of the Carboniferous along the 

 southeastern flanks of the range has been considered by 



