Vol. 51.] PHYSICAL FEATURES AND GEOLOGY OF MAURITIUS. 467 



Underground rivers are common wherever there are lava-beds, 

 and some have been met with at great depths ; on the La- 

 bourdonnais estate one was tapped at a depth of 92 feet, and 

 another was found on sinking a well near Grand Bay, at a depth of 

 .70 feet. 



Among the cliffs which form part of the coast are several re- 

 markable natural curiosities. One of the finest of these is a blow- 

 hole called the Souffleur ; it is in a high lava peninsula, honey- 

 combed beneath with caverns into which the sea rushes. In the 

 roof of one of these is a hole about 2 feet in diameter, up which the 

 water is forced, when the height of the waves is great enough, 

 .generally when the wind is from the south. The water rises in a 

 magnificent jet, 60 or 70 feet high, with a roar like thunder that 

 shakes the cliffs around. The top of the jet curves over, and falls 

 like an enormous drooping ostrich-feather. 



Another curiosity is the Pont Naturel, a double-arched bridge 

 with two spans of about 25 feet each, and supported iu the middle 

 by a natural pillar 30 feet high. This has been caused by the roofs 

 of two contiguous caverns being broken through, leaving a narrow 

 piece of their roofs standing, supported on part of the original 

 ■division between them. The sea roars through the bridge and into 

 the cavern beyond, sending up clouds of spray, and slowly but 

 surely eating away the supports. 



The next extensive tract of lava-flows is in Flacq and the 

 npper parts of Moka. They all apparently have issued from the 

 craters of Maccabee, Baisse, Grand Trou North, and the Caves. For 

 several miles along the slopes there are no rivers, marshes abound, 

 and caverns — generally containing water — are of frequent occur- 

 rence. The lower part of these lava-flows, called the Plaine des 

 Roches, is nearly flat, and here the molten rock has spread out in 

 sheets, which in many places are only a foot or two thick, and 

 cover a stratum of ash. These lava-flows are full of caves and 

 steam-holes ; one of the latter, called the ' Puits des Hollandais,' is 

 •worthy of notice. The hole is nearly circular, with a bell-mouth, 

 ; and about 35 feet across. It is filled with water to within 15 feet 

 •of the ground-level. The sides are perfectly vertical, and the 

 author found the depth with a sounding-line to be from 82 to 86 

 feet in different parts. The water is beautifully clear and fresh, 

 and, strange to say, its level has never been appreciably altered, 

 although a steam-pump, now disused, withdrew a 6-inch stream 

 night and day for a year and a half for irrigation purposes. It is 

 a curious fact that there is a pass in the reef just opposite the Puits 

 des Hollandais, although there is no stream on the surface. Unless 

 we adopt the supposition of a large subterranean reservoir being in 

 connexion with this hole, which keeps it at the same level, and also 

 flows to the sea by underground channels, it is difficult to account 

 for the phenomena. 



In the Plaine des Roches, near Roche Noire, are two caverns 

 containing running water, which formerly was pumped up for 



