urioN.] BASALTS OF THE UINKARKT. 123 



sensibly horizontal strata left by the denudation of the same beds from 

 the platform surrounding. It is roofed over with a ponderous lava-cap, 

 500 to 800 feet thick. Under this lava-cap arc seen in numerous places 

 the horizontal edges of the strata, though the flanks of the mountain 

 are so thickly covered with the debris formed by the disintegration of 

 the basalts at the summit that these strata are for the most part buried. 

 The beds beneath the lava are of Permian age, and it is evident, that 

 nearly the whole and possibly quite all of the Permian series remains 

 in the mountain mass. That these basalts are very old is evident at a 

 glance. The evidences of erosion are seen on every hand, and their 

 aspect is strikingly different from that of the younger or middle aged 

 basalts. On the summit of the mountain we find a cluster of old vents, 

 from which a great part at least of these lavas were expelled. They are 

 simply large craters torn down, dissolved and rotted away to their very 

 roots by the ravage of time. It is evident, too, that the lava -cap itself is 

 as a whole a mere remnant of a mass of superposed sheets which once 

 extended much beyond the steep ledge which now limits them all around 

 the mountain. The geologist draws his conclusion very quickly. These 

 basalts in the lava-cap were extravasated at a time when the aspect of 

 the surrounding country was very different from that which is now pre- 

 sented. At that time large bodies of Permian strata, since swept away 

 extended continuously from the edges now exposed in the mountain 

 ilanks over spaces far away from it. AVe cannot indeed affirm that the 

 great denudation had not already begun its havoc in the Permian, 

 but we may be sure that it had not reached nearly its present stage. 

 Mount Trumbull then is a remnant of a platform of lava-capped Permian 

 beds, which was once of much greater extent. What was the extent 

 of this platform at the time of the eruptions, we do not yet know, nor 

 are we likely to know. 



Around the base of the mountain on all sides the moie recent craters 

 are thickly clustered. The cones are for the most part in an admirable 

 state of preservation ; though here and there one may be found which 

 has suffered considerable ravage. About two miles north of the base of 

 Trumbull, especially, is an old cone, which has been laid open in such a 

 manner as to disclose its interior structure very clearly. It is in all 

 respects similar to the cones of the Mediterranean islands and countries. 

 All of these craters were built at a much later period than the lava-cap 

 of the mountain. 



Mount Logan which lies near Trumbull to the southwestward, pre- 

 sents a similar state of affairs. It is a tabular mass capped with the 

 more ancient basalts and with a great body of Permian beds beneath. 

 South of Logan is another mass of ancient basalts, overlying Permian 

 strata. Upon this southern table, however, are planted some well 

 preserved craters which belong to the middle age of eruptions. Chief 

 among these is Mount Emma, whose summit has been used as a pri- 

 mary topographical station. In general, these more ancient basalts 



