3 2o THE ROMAN CAMPAGNA 



fall short of the total extent of the post-Pliocene 

 uplift of the Apennine chain. 



Not improbably the deep and extensive erosion of 

 the Pliocene formations before the deposition of the 

 volcanic tuffs, and their elevation above sea-level were 

 related phenomena, connected with the outbreak of 

 the remarkable volcanic episode in the geological 

 history of Central Italy, which has so profoundly 

 modified the scenery of the country. In the yellow 

 sands and gravels of Monte Mario no trace of 

 volcanic detritus has been detected. Their sediments, 

 containing pebbles of Rhaetic, Jurassic and Cretaceous 

 rocks can hardly have come from any other source 

 than the Apennine chain. But before their deposition 

 had quite come to an end the Volcanic period was 

 ushered in which forms the second stage of the 

 history of the region. 



II. We have now to deal with the records of one 

 of the most interesting phases in the evolution of 

 the framework of Italy — the period that witnessed 

 the birth, development and extinction of a series 

 of volcanoes which, starting on the sea-bottom in 

 front of the western coast, gradually built up a tract 

 of plains in some places thirty to forty miles broad 

 and altogether perhaps as much as 200 miles long, 

 finally crowned with majestic cones several thousand 

 feet high. The chronicles of this episode being 

 tolerably complete in the Roman Campagna, they 

 enable us to follow the course of events with great 

 clearness from the beginning to the end. 



Nowhere in the district around Rome have the 

 earliest indications of the oncoming of this volcanic 



