Formations on the Left Bank of the Rhine. 157 



actly the same general characters as those just described, but 

 remarkable for its large dimensions and extreme regularity. 

 The ridge of fragmentary matters, "which girds it in, is with- 

 out a break, and nearly every where preserves a uniform level 

 at about 150 feet above the water surface. The depth of 

 the lake is above 300 feet ; the sides slope in the interior 

 at an angle of about 45°, on the exterior of 35°. Immediate- 

 ly at the foot of the cone of the Polvermaar, on the south 

 side, rises a hill containing a much smaller crater, with a peat- 

 bog at its bottom. 



Still farther south, between the villages of Strohn and 

 Trittschied, is a double cone of large dimensions. It has two 

 considerable craters, both broken down towards the N. W. 

 The southernmost is large and circular, and bottomed by a 

 morass. The other has produced a current of basaltic lava, 

 which, after forming some considerable hummocks in a N. W. 

 direction, turns its course along the bed of the neighbouring 

 rivulet to the S. W., and occupies its channel to a distance of 

 two miles or more, crossing the great Coblentz road. 



But unquestionably the group of volcanic vents, which pre- 

 sents the greatest interest of all in the Eiffel district, is the 

 Moseberg near Bettenfeld, with the neighbouring Meerfelder 

 Maar. The Moseberg is one of the highest hills of the whole 

 country. Its base up to a considerable elevation above the 

 level of the plain around, consists of greywacke slate and red 

 sandstone. Its summit is formed by a triple volcanic cone, 

 the accumulated ejections of three small craters, which remain 

 very distinct. The two most northerly ones are entire, and 

 reduced to the state of peat-marshes. The third has been 

 broken down on its south-east side by a current of lava, of 

 very recent aspect, which, issuing from the breach, descends 

 the slope of the mountain in a stony flood, until it reaches the 

 bed of a small river below. 



The lava and scoria? of these cones, have enveloped a great 

 quantity of half-fused fragments of sandstone and slate. The 

 circular crater, called the Meerfelder Maar, is remarkable for 

 its vast size and depth. It has been hollowed out of both the 

 transition-slate and red sandstone, forming the north base of 

 Moseberg ; and the steep walls which encircle it, exhibit, on 



