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PROCEEDIlfGS OF THE GEOLOGICAL SOCIETY. [April 14 



ting. The greater part of each vein is " dead " or unproductive ; 

 the productive portions or " pockets " vary from a few yards to 100 

 fathoms in length and from a few inches to nearly 30 feet in thickness. 

 The pockets are sometimes very close together, sometimes more than 

 a mile apart in the same vein ; in all cases they are connected hy a 

 vein-" track," consisting chiefly of softened clay-slate and quartz 

 with occasionally a little iron-ore (fig. 2). 



The " pockets " are found not to descend parallel to the line of 

 their dip, but to slope endwise, generally to the west, but in one or 

 two cases to the east. To this phenomenon the author gives the name 

 of " end-slant." He accounts for it in the following manner. He 



Fig. 2. — Longitudinal Section of a Vein. 



P i 'P 



P 



V t P t V 



ppp. " Pockets." ttt. Vein-track. 



P 



assumes that the veins have been segregated from the adjoining clay- 

 slate, the unproductive portions occurring where the continuous 

 strata were not sufficiently impregnated with ferruginous matter to 

 produce a lode of ore, the " end-slant" of each productive part being 

 " determined by the line of intersection of the sloping plane of the 

 vein with the boundaries of the ferruginous portions at the com- 

 mencement and termination of each * pocket.' " 



Discussion. 



Mr. Etheeidge thought that the great iron-lodes of this district 

 lay in the great faults which traverse the country, and in which 

 there had been considerable downthrow to the north. In most 

 cases in the Bristol district the lodes seem to have been formed at 

 the bottom of the sea during the New-Red-Sandstone period by 

 infiltration of salts of iron into the faults. 



3. On the Salt-mines of St. Domingo. By F. Rttschhaupt. 

 (Communicated by Sir R I. Murchison, Bart., K.C.B,, F.E.S., Y.P.G.S.) 



[Abridged,] 



The author described the Cerro de Sal, or Salt-mountain of St. 

 Domingo*, as subordinate to the main chain of mountains run- 

 ning in a S.E. and N.W. direction, its own direction being E.S.E. 

 and W.N.W. The eastern part of the Cerro de Sal is very rugged 

 and steep, rising to 550 or 600 feet; towards the W. it becomes 

 lower, and forms a chain of irregular hills. 



* See Quart. Journ. Geol. Soc. vol. xxiv. p. 335. 



