Ch. XIV.] 



TRASS OF RHINE VOLCANOS. 197 



occurs the Pulvermaar of Gillenfeld, an oval lake of very 

 regular form, and surrounded by an unbroken ridge of frag- 

 mentary materials, consisting of ejected shale and sandstone, 

 and preserving an uniform height of about one hundred and 

 fifty feet above the water. The side slope in the interior is 

 at an angle of about 45; on the exterior, of 35. Volcanic 

 substances are intermixed very sparingly with the ejections 

 which in this place entirely conceal from view the stratified 

 rocks of the country *. 



The Meerfelder Maar is a cavity of far greater size and 

 depth, hollowed out of similar strata ; the sides presenting some 

 abrupt sections of inclined secondary rocks, which in other 

 places are buried under vast heaps of pulverised shale. I 

 could discover no scoriae amongst the ejected materials, but 

 balls of olivine, and other volcanic substances are mentioned as 

 having been found f- This cavity, which we must suppose to 

 have discharged an immense volume of gas, is nearly a mile in 

 diameter, and is said to be more than one hundred fathoms 

 deep. In the neighbourhood is a mountain called the Mose- 

 berg, which consists of red sandstone and shale in its lower 

 parts, but supports on its summit a triple volcanic cone, while 

 a distinct current of lava is seen descending the flanks of the 

 mountain. The edge of the crater of the largest cone reminded 

 me much of the form and characters of that of Vesuvius. 



If we pass from the Upper to the Lower Eifel we find the 

 celebrated lake-crater of Laach, which has a greater resem- 

 blance than any of those before-mentioned to the Lago di 

 Bolsena, and others in Italy being surrounded by a ridge of 

 gently sloping hills, composed of loose tuffs, scoriae, and blocks 

 of a variety of lavas. 



Trass and its origin. It appears that in the Lower Eifel 

 eruptions of trachytic lava preceded the emission of currents 

 of basalt, and that immense quantities of pumice were thrown 

 out wherever trachyte issued. In this district, also, we find 



* Scrope, Edin. Joura. of Sci., June 1826, p. 145. 

 f Hibbertj Extinct Volcanos of the Rhine, p. 24. 



