J. P. Lesley — Origin of Pipe Ore. 459 



V. — Origin of Pipe Ore. 

 By J. P. Lesley, of Philadelphia. 



THE following account of the discovery of an underground lake 

 in Algeria went the rounds of the newspapers in July, 1879. 



The Tlemcen Courier (Algeria) describes a wonderful discovery recently made at 

 the picturesque cascades of that place. Some miners had blasted an enormous rock 

 near the cascades, and, on removal of the debris, found it had covered a large 

 opening into a cave, the floor of which was covered with water. Constructing a 

 rude raft, and providing themselves with candles, the workmen sailed along this 

 underground river, which, at a distance of 60 metres, was found to emerge into a 

 large lake of limpid water. The roof of the cavern was very high, and covered with 

 stalactites, the brilliant colours of which sparkled under the light of the candles. 

 Continuing their course, the workmen had, at certain places, to navigate their craft 

 between the stalactites, which, meeting stalagmites from the bed of the lake, formed 

 enormous columns, which looked as if they had been made expressly to sustain the 

 enormous arches. They thus reached the extremity of the lake, where they noticed 

 a large channel extending toward the south, into which water quietly made its way. 

 This is supposed to be a wide fissure which has baffled exploration hitherto at 

 Sebdon, and which connects the cascades with that locality, and thus with the 

 mysterious sources of the Tafna. It is possible that here they have found an 

 immense natural basin, supplied by powerful sources, and sending a part of its 

 waters towards the lake, while the rest goes to Sebdon. The workmen estimated 

 the distance underground traversed by them at three kilometres, and the breadth of 

 the lake at two. They brought out with them a quantity of fish, which swarmed 

 round the raft, and which were found to be blind. 



Whatever exaggerations may have been indulged in by the 

 reporter of the discovery described above, I think that it is worthy 

 of the thoughtful attention of geologists, for several reasons : — 



1. It offers a rational solution of the problem how the roofs of 

 wide caverns in limestone regions have been, and still are, supported. 



2. It supports the views which I have repeatedly published re- 

 specting the prime agent for determining the topography of the 

 earth's surface, viz. the dissolution of the limestone formations, the 

 letting down of the over-rocks, and the gradual withdrawal of the 

 outcrops from each other on opposite sides of anticlinals ; and in 

 steps determined by the limestone formations. 



3. It clears up the chief obstacle to a rational theory of the genesis 

 of our pipe-ore deposits ; and this is why I invite to it the attention 

 of my fellow-geologists in Great Britain, hoping to get from them 

 expressions of assent or dissent. 



In the larger limonite mines of Pennsylvania, botryoidal ore 

 masses occur, the origin of which has never been explained. The 

 older mines are now open quarries, hundreds of yards long and 

 wide, and from 50 to 150 feet deep ; of irregular shapes ; surrounded 

 by walls of massive limestone ; and floored with mud and standing 

 water. They are vast pots in the Lower Silurian or Siluro- 

 Cambrian Magnesian Limestone formation, No. II. of our old survey, 

 the Calciferous and Chazy formations of the New York and Canada 

 reports. Many of them have been excavated to their beds ; all the 

 iron ore removed, and the mine abandoned. Others still hold 

 unknown quantities of limonite beneath the mud floor, as shown by 

 trial bore-holes. 



The clay which filled (and partly still fills) such a mine is 



