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HARDWICKE'S SCIEN CE -GO SSIP. 



of Albano. Along this part of the road the tra- 

 veller is struck by the view on his right hand, for 

 beneath him stretches a richly-cultivated plain, 

 hemmed in on all sides but the south-western by 

 hills, and exhibiting unmistakable marks of the site 

 of an old lake : it is in fact an old crater-lake eight 

 miles in circumference, the crater of some long 

 extinct volcano converted first into a lake (which it 

 seems not unlikely was its condition in the days of 

 Strabo), and then, being drained, into a most fertile 

 plain : this is backed by the picturesque town of 

 Ariccia with its handsome viaduct forming connec- 

 tion with Albano. 



Passing through Albano, the site of the villas of 

 Pompey and Domitian, an interesting section 

 presents itself just before crossing the viaduct; 

 here a very coarse and loose ash overlies a fine and 

 compact muddy ash, and in the former are many 

 fragments of white crystalline limestone, fragments 

 which must have been torn from some of the lime- 

 stone rocks through which the volcanic vent was 

 opened, and have fallen with the various fragments 

 of lava, pumice, and fine powder, round — though at 

 some distance, probably, from — that vent. Prom the 

 viaduct itself a beautiful view is obtained : on the 

 one hand up a well-wooded vale, with the Alban 

 Mount towering in the background ; and on the 

 other, over the old crater-lake of Ariccia to a 

 belt of flat campagna, and the blue Mediterranean 

 beyond. 



Prom Ariccia the shortest way to the summit of 

 the mountain is through the beautiful woods 

 clothing its sides, along tracks worn in the soft 

 white crumbling ash, into which stream-courses 

 have deeply cut, and which forms a soil of light 

 powder, with innumerable sparkles of mica-flakes 

 and augite crystals. Before the summit is gained 

 some beautiful glimpses of the Alban Lake are 

 obtained through the surrounding wood ; a lovely 

 basin of water six miles in circumference, closely 

 surrounded by the old crater cliffs, for this too is 

 an old crater, upon the edge of which is happily 

 placed the village of Castel Gaudolfo 460 ft. above 

 the level of the lake. Monte Cavo, as the summit 

 of the Alban Mount is called, is 3,130 ft. above 

 the level of the sea, and forms the highest point of 

 the circular crater of the old volcano. The view 

 from it is exquisite ; the crater-lakes of Albano and 

 Nemi ; picturesque villages aptly perched upou 

 rocky prominences or swelling hills ; the old crater- 

 walls, and the far older crater-walls beyond them . 

 the snowy Apennines ; the flat Campagna, where im- 

 perial Rome still sits defiant; the old volcanic 

 hills and crater-lakes (Bracciano, &c.) beyond ; the 

 blue waters of the Mediterranean ; — all go to make 

 up a panoramic picture of surpassing and peculiar 

 beauty. 



Standing then on the summit of Monte Cavo one 

 sees at one's feet a capital type of a normal volcano ; 



most evident are the crater- walls, perfect on all sides 

 except towards Rocca di Papa, and inclosing a 

 circular plain, where, according to tradition, 

 Hannibal encamped when marching against Rome. 

 In the centre of this plain rises a small but well- 

 formed cone, while far beyond the crater-walls, 

 but rudely parallel to them, is a line of hills marking 

 the boundary of a much older and larger crater, a 

 giant in its time. 



Descending the crater-walls on their inner side, 

 many sections may be examined which reveal their 

 structure, and show them to be made up almost 

 wholly of beds of ash and scoriae conglomerate, 

 dipping outward, the result of ejection from, and 

 falling round, a central orifice. Some of the ash, 

 for the most part white, is very finely laminated, 

 caused by its mixture with water and consequent 

 muddy character ; such beds, however, alternate 

 with others of very loose scorise, resembling heaps 

 of clinkers. Oa the side of Rocca di Papa— one of 

 those happily-placed mountain villages, the site, 

 moreover, of the ancient Pabia — where the crater- 

 wall is broken down, there have issued two streams 

 of leucitic lava, one of which flowed nearly as far 

 as the present site of Rome, the other south-west- 

 ward to Ardea. An excellent section of one of 

 these lava-flows is seen in the bold rocky cliff imme- 

 diately below which the village is built. It is a 

 dark grey rock, formed of augite and leucite, the 

 leucite crystals being conspicuous, and rests upon a 

 bed of fine yellow and black ash some 20 ft. thick, 

 dipping away from the crater in a north-west direc- 

 tion, at an angle of 26°. 



At several points on descending through Rocca 

 di Papa the beds may be seen with the same high 

 outward dip, and even as far as Prascati their 

 general inclination is markedly away from the 

 central crater of Monte Cavo. In places, 

 however, these ash and ash-mud beds have been 

 disturbed and thrown into gentle curves. In a 

 cutting at Prascati station is a coarse volcanic 

 breccia, many of the blocks being of considerable 



size. 



The points then specially to be noted from such 

 a brief examination of this ancient volcano are :— 



1. Its typical structure,— two craters, an old and a 

 more modern, and a central cone ; the crater-walls 

 and the modern cone all formed, in the main, of 

 outwardly-dipping beds. 



2. The small proportion of lava-currents as com. 

 pared with the great bulk of ejected materials, that 

 seem to form the mass of the mountain. 



3. The ejected materials have a wide spread, and 

 consist of what must have been liquid ash-mud, and 

 loose dry ash and scoriae. 



4. The many old crater-lakes around seem to have 

 been all more or less connected with the principal 

 volcanic mountain, Monte Cavo. 



J. Clifton Ward. 



