160 Notes on the Geology of the 



waters of Middle Arm Creek from those running south in the 

 neighbourhood of the Ilfracombe lode. 



The question as to whether or not coal is likely to be 

 found in the district is an exceedingly puzzling one. Very 

 little, if any, prospecting for it has been done ; but just before 

 leaving Tasmania I heard of a 15-inch seam having been 

 found a few miles south of Exeter, higher up the River 

 Tamar, on John Plummer's ground, north of Rosefairs, but 

 I had no time to examine into the reliability of the state- 

 ments made. 



The country to the east of the river consists of greenstone, 

 with underlying carboniferous rocks, but Mr. Gould's map 

 gives no indication of any coal seams. 



Coal occurs on the Mersey, Don, and Forth rivers to the 

 west, and at Fingal and Mt. Nicholas to the east. The 

 Fingal coal measures are overlaid by greenstone and under- 

 laid by upper palaeozoic marine beds, containing fossils 

 identical with those in the district I am describing. The 

 seams are from six to eight feet thick, but the coal is of 

 indifferent quality. The Douglass River coal is of better 

 quality, but the percentage of ash is high. In Mr. Gould's 

 report on the Mersey River coalfield, dated 29th October, 

 1861, page 7, he states, in regard to the Denison colliery, 

 that " A dark blue clay, slightly calcareous, and intermixed 

 with sand and mica, is thrown down, by a large fault, 

 against the coal seam. It is highly fossiliferous, contain- 

 ing orthonota, spirifera, pachydomus, fenestella, encrinites, 

 &c, &c. From this and other lithological differences in the 

 strata, it appears that the coal here underlies the fossili- 

 ferous beds ; at Coal Creek, the Mersey Coal Company's 

 shaft was sunk entirely through fossiliferous beds. The 

 seams are greatly faulted." 



The fossiliferous marine beds south of Yorktown would, 

 by a calculation of their dip, supposing no faulting to occur, 

 underlie the British and Tasmanian Charcoal Iron Com- 

 pany's works at Port Lempriere by over 5000 feet ; but it is 

 evident by an inspection of the dip of these beds at dif- 

 ferent localities that such a fault or faults must occur. The 

 angle of dip varies very greatly, being larger at the edges 

 of the basin where the rocks are tilted up than towards 

 the centre at Middle Arm. At Middle Island the dip is 

 reversed, so that the thickest part of the basin is probably 

 in the neighbourhood of Port Lempriere. 



Of the greenstone little need be said. It has been spread 



