W. A. E. Ussher — Pleistocene Geology of Cornwall. 253 



Stream Tin Sections. 



1. De la Beche (Report, p. 405) says that in the interior the tin 

 ground is usually covered by river detritus, more open spaces fre- 

 quently having a bed of peat (in which oaks are common) interposed 

 between the tin ground and other detrital accumulations, as in 

 Tregoss Moor and the moors adjacent to Hensborough. " In some 

 whole ground (stream tinners' term for stanniferous gravel) and 

 superincumbent beds not previously disturbed by the old men, upon 

 Bodmin Coast Moor, the peat beds with oak, alder, etc., covering 

 the tin ground very irregularly, were in some places several feet 

 thick, in others absent, though on the whole they seemed to keep a 

 somewhat common level above the tin ground. In some places thin 

 peat beds had been accumulated at still higher levels among the 

 gravels, sands, and clays. The shelf composed of semi-decomposed 

 granite was very irregular, holes 30 or 40 feet deep presenting 

 themselves, in the bottoms of which there was usually good stanni- 

 ferous gravel." 



2. Mr. Pattison (op. cit.) gives a section of the Fowey Valley Works, 

 in which the (hard and black) forest bed was met with at from 

 23 to 27 feet below the surface, resting on stream tin gravel, and 

 overlain by sand with a peat bed containing ferns and hazel. 

 The granite shelf, tin gravel, and forest bed presented a faulted 

 appearance. 



3. Par. De la Beche (Beport, p. 403). In cutting the Par Canal 

 at Pons Mill, near St. Blazey, granite blocks, as if arranged for a 

 bridge, were found beneath 20 feet of gravel, probably in part 

 resulting from stream tin washing. Section in low ground near the 

 Par Estuary — 



1. Eiver deposits 1ft. 6in. 



2 and 3. Mud, sand, clay, stones, much disturbed by tbe 

 stream tinners in the upper part; with vegetable 

 matter in the lower part loft. Oin. 



4. Fine sand with sea shells like cockles, and rolled 



pebbles in the upper part 4ft. Oin. 



5. Mud, clay, sand, wood, nuts, etc., mixed 3ft. Oin. 



6. Tin ground resting upon an uneven surface of slate ... 6in. to 6ft. Oin. 



4. North of St. Austell. Mr. Henwood gives the following 

 sections. The letters prefixed denoting beds probably contempor- 

 aneous. (T.R.G.S. Corn. vol. iv. pp. 60 to 64.) 



A. Merry Meeting, in parish of St. Boche. 



a. Mud, with decayed vegetable matter 2ft. to 3ft. 



1. Granitic gravel - 2ft. 



2. Silt, with decayed vegetable matter and plates of mica ... 4ft. to 5ft. 



b. Granitic stones, gravel and sand mixed with silt and nuts ... 4ft. 



3. Vegetable matter (locally called Fen), moss, grass, wood 



(? charred) 1ft. 



4. Silt (vegetable remains ?) 1ft. 



5. Vegetable remains (charred like No. 3) 1ft. to 3ft. 



6. Vegetable matter passing into silt Sin. to 1 Oin. 



c. Tin ground, with enormous quartz blocks, some 15 ft. square ; 



tin ore as sand, stones, and pebbles mixed with quartz, 

 granite, and schorl rock ; little rounded, and of the best 

 quality where the decomposed granite shelf is softest 4ft. to 30ft. 



