April 21, 1898] 



NA TURE 



58. 



THE PHLEGR^AN FIELDS. 



THE fired rocks and hills of volcanic origin stand in 

 so striking a contrast to those of aqueous origin, 

 that they have exercised a very powerful influence on the 

 thoughts of man in all ages. Frequently associated with 

 such formations are the phenomena which we are accus- 

 tomed to refer to as volcanic — " Ijurning mountains," boil- 

 ing springs, gaseous exhalations, terrifying noises— all 

 shrouded with a mystery which demands explanation. 

 Even in a locality in which the volcanic fires have been 

 extinguished or have long remained quiescent, the peculiar 

 configuration of the ground often keeps alive the tradition 

 of former outbursts of subterranean fire, and the tradition 

 usually supplies the explanation of the configuration. 

 The ancient Romans, long before the awful catastrophe 

 of A.D. 79, seem to have been quite aware that Vesuvius 

 had not always been in a condition to support the rich 

 cultivation which covered its slopes in their day. It is 

 only in rare cases that the inquirer is rewarded by find- 

 ing that the history of a heap of burnt soil is preserved ; 

 more often he will hear vague stories 

 of the direful effects of prehistoric 

 struggles of Cyclops or other mytho- 

 logical monsters. 



In a recent research ^ I have en- 

 dea\oured, by examining the marks 

 with which the Phlegraean Fields are 

 scored, like a much over-written 

 palimpsest, to collect materials for a 

 history of the alterations which the 

 surface of the country has undergone. 

 Within the Phlegrsean Fields, west of 

 Naples, only two volcanic structures 

 have been formed within the historical 

 period. For trustworthy information 

 respecting all structures but the Monte 

 Nuovo and the lava stream from the 

 Solfatara we are entirely dependent 

 upon the facts collected by the geolo- 

 gist and the geographer. In my work 

 I was chiefly guided by the desire of 

 estimating how far the existing super- 

 ficial configuration or morphography 

 of a volcanic region is an indication 

 of the past history of its development. 

 With this end in view purely topo- 

 graphical features, selected accordmg 

 to certain principles, were studied, 

 and from them a theory of their origin 

 and relative age was constructed. The 

 results obtained by the method admit of being tested by 

 the results of geological research whenever the latter is 

 possible. 



The importance of a method which will yield in- 

 formation respecting the past history of a volcanic 

 country from a mere superficial examination is very con- 

 siderable. The volcanic regions of the sea-bottom and 

 of the moon are alike inaccessible, to the stratigraphical 

 geologist. The only kind of information obtainable is 

 that respecting the superficial configuration ; and there- 

 fore it is of the greatest importance that the value of a 

 method which will enable us to utilise this information, 

 in reading the records of the past, should be carefully 

 estimated by experiment within the sphere of the 

 geological critic. 



The Phlegraean Fields are well suited for the trial of 

 such a method, because within a small area the face of 

 the country records the results of long-continued volcanic 

 activity and of denudation both by sea and rain. Within 

 an area of not much more than fifty square miles are 

 collected the assemblage of volcanic vents and crater 



1 "The Phlegraean Fields." By R. T. Gunther. (fieosraphical Journal, 

 1897, vol. X. pp. 412-435, and 477-499, with 8 maps and 15 figures.) 



walls, the presence of which distinguishes the Campi 

 Flegrei from the adjoining level plains of fertile volcanic 

 soil of the Campagna Felice, stretching right away inland 

 to the limestone slopes of the Apennines. 



By far the most important topographical features 

 within this region are composed of loose ashes or of 

 compacted tufa. Lava-streams or heaps of lava charac- 

 teristic of so many other volcanic regions cover but a 

 small part of the surface of the country at the present 

 day ; in the future, no doubt, their harder, more resistent 

 qualities will cause them to stand more prominent when 

 the forces of denudation have removed the super- 

 incumbent layers of more readily erosible tufa. 



Many of the hill forms are readily reducible to the 

 simple type of a volcanic crater wall surrounding a 

 crater, such as is naturally formed by fragmentary 

 materials ejected from a vent and allowed to fall uniformly 

 around that vent. In the Phlegraean Fields there are 

 five almost perfect examples of such volcanic ring walls. 

 Of these, Monte Nuovo is still to be seen in much the 

 same condition as it was immediately after its eruption 



Fig. 



Crater of Astroni from the North-East. In the distance is part of the crater wall of 

 Archiagnano culminating in the Torre Nocera. 



in September 1538. The Fossa Lupara, Solfatara, 

 Astroni and Cigliano are hardly less perfect examples of 

 typical volcanic craters. The topographical aspect of 

 all is identical. In each a crater is entirely surrounded 

 by an almost circular wall, which has a steep and some- 

 times precipitous crater-slope on the inside, but a more 

 gradually inclined cone-slope on the outside. 



In addition to these hills, which are volcanic cones of 

 the first rank of symmetry and preservation, there are 

 others which are not less certainly volcanic cones 

 produced in the same way, but which have had their 

 symmetry marred by the removal of their flanks, either 

 by marine erosion or by destructive eruption from an 

 adjacent volcanic vent. The walls of the craters of 

 Capo Miseno, Porto Miseno, Bacoli, Campiglione and 

 Nisida, have all been more or less removed on the side 

 turned towards the sea, and, with the exception of the 

 Campiglione crater wall, are still being eroded away at 

 the present time. The craters of Porto Miseno and 

 Nisida are submerged, and being in communication with 

 the open sea by breaches in their walls, afford good 

 harbours for small vessels. The floors of the other 

 craters are above sea-level. On the other hand, the 



NO. i486, VOL. 57] 



