522 MB. E. GILPIN ON THE GEOLOGr OF 



and prostrate Sigillarice, with roots attached and growing into the 

 coal, are seen in these shales. Trunks have been observed nearly five 

 feet in diameter, but they do not usually exceed two feet. The term 

 *' marl " is here applied, not to beds necessarily calcareous, but to 

 red and green shales which crumble on exposure. Sandstone-beds, 

 grey and white in colour, and often fifty feet in thickness, are met 

 at frequent intervals, and nearly always occur a few feet above the 

 coal-beds. Many of the beds are calcareous, and are then flaggy, 

 micaceous, and sometimes ripple-marked. Almost invariably under- 

 clays, highly charged with roots and rootlets, occur under the coal- 

 beds, but in a few cases the coal-seams rest directly on thin beds of 

 fossiliferous limestone, and, in one case, the floor is sandstone. The 

 coal-beds do not merit any particular notice, being similar in many 

 points to those of the Durham coal-field. 



Millstone Gkit. 



The division -line between this formation and the Productive 

 Measures is. entirely an arbitrary one, and, as marked on the Geo- 

 logical Survey maps, is regarded by many as encroaching on mea- 

 sures that may fairly, so far as their coal contents are concerned, 

 bo considered productive. This is borne out by the fact that a col- 

 lection of fossil plants, from a point apparently low down in this 

 horizon, about two miles east of Sydney, shows species, according 

 to Sir J. W. Dawson, occurring only in the Productive Measures, 

 and especially in its higher beds. 



As compared with the higher division, these strata show a much 

 larger percentage of sandstones, frequently coarse and sometimes 

 felspathic, fewer argillaceous beds, and much false stratification; 

 and this formation is specially distinguished from those lying above 

 .and below it by the absence of calcareous matter. IS'ear the old 

 syenitic and felsitic rocks the prevailing colour is red; further 

 away, where the material has been derived from the preceding Car- 

 boniferous horizons, grey shales are met with. The maximum thick- 

 ness in this district is 5700 feet, but it rapidly diminishes towards the 

 north, until at Cape Dauphin only 500 feet are found. Numerous 

 coal-seams are met, some of workable size and persistent for long 

 distances. The long arm of Millstone Grit, extending up the Salmon 

 and Gaspereau rivers, contains several thin seams of coal, and may 

 represent the formation as developed east of Sydney. 



The Carbonipeeous Limestone. 



In the Sydney district this formation occupies a triangular tract 

 of country between the two arms of Sydney Harbour, and attains a 

 thickness of about 2000 feet. It is composed principally of red and 

 grey shales, sometimes approaching marls in aggregation, argillaceous 

 and calcareous, and frequently carrying nodules of ironstone and 

 limestone. Numerous beds of limestone are met, compact, lami- 

 nated, or concretionary, usually grey and blue in colour, but some- 

 times black and bituminous ; these are frequently associated with 

 beds of gypsum and auhydrite, in some parts of the island over 



