146 Proceedings of Philosophical Societies. [Feb. 



killas), and in the immediate vicinity of the mines which have 

 recently been opened in that part of the county. 



In 1803 an Act of Pariiament was obtained for cutting a canal 

 from the town of Tavistock to Morwelham, a quay on the river 

 Taraar. An essential part of this plan was a tunnel through hard 

 rock, abiut a mile and three quarters in length ; passing through 

 Morwel Down at an average depth, from the surface of about 400 

 feet, and in a direction calculated to cut through all the E. and W. 

 or metalliferous veins that might traverse the hill. Of this important 

 undertaking somewhat less than one-fourth remains to be per- 

 formed ; but the portion already executed has disclosed several 

 important geological facts, which are detailed in this paper, and in 

 the section and specimens by which it is accompanied. 



Six beds or dykes have been cut through, the thickness of which 

 varies from six to 26 fathoms. Their direction is inclined to that of 

 the metalliferous veins, and they dip pretty uniformly to the North ; 

 they are composed of clay-porphyry, of another variety of por- 

 phyry, of quartz, and of quartz mixed with chlorite. 



Several metallic veins, some of them already productive, and 

 affording copper, and in a few instances tin, have also been disco- 

 vered ; they traverse all the strata, and exhibit a remarkable 

 difference in their dip or under-lay on the two sides of the hill, 

 those on the north side dipping to the north, and those on the south 

 side dipping to the south. 



Ma!/ 20. — A communication from Lord Webb Seymour was 

 read. 



This paper is accompanied with explanatory drawings, and 

 describes an instrument of his Lordship's invention called a clino- 

 meter, for the purpose of determining the position of the planes of 

 stratification. The instrument itself had been previously presented 

 to the Society. 



A paper, accompanied with specimens, containing mineralogical 

 remarks on part of the settlements of the Hudson's Bay Company, 

 compiled from the reports of several observer?, by the Earl of 

 Selkirk, was read. 



From Mr. Aulds it appears that the bed of Nelson river, seven 

 miles below Hamborough Head, and not far from its mouth, presents 

 several rapids, which are formed by flat strata of lime-stone, and in 

 one instance by whin-stone (probably one of the trap rocks by 

 which stratified lime-stone is so often accompanied). The effect of 

 the ice floods in this river is very remarkable. The water charged 

 with pieces of ice appears to be capable of detacliing large blocks 

 of lime-stone, and conveying them to a considerable distance. A 

 deposite of this kind, the work of a single season, is described as 

 forming a shoal 200 or 300 yards in length, and consisting of small 

 Stones covered by several hundred blocks of the same kind, weighing 

 several tons each, and four feet and more in thickness. 



There is reason to believe that tlie same lime-stone formation 

 Pilends through all the country west of Lake Wimpic, as far as the 



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