316 THE ROMAN CAMPAGNA 



with the adjustment of the aqueduct of the Aqua 

 Vergine. Only a few feet below the crowded pave- 

 ments of that busy thoroughfare lies the old sea- 

 bottom with its abundant relics of marine life. In 

 borings for water which have been made around Rome 

 the same deposit has been ascertained to extend below 

 the later volcanic formations of the Campagna. Thus 

 at the Appia Antica fort, near the tomb of Cecilia 

 Metella, the clay was entered at a depth of about 

 300 feet from the surface or eighty feet below the 

 level of the sea. As the upper limit of the clay at 

 Monte Mario lies about 200 feet above sea level and 

 the distance from that outcrop to the fort in question 

 is about six miles, it might be inferred that there is 

 here evidence of a southeasterly dip of the deposit 

 amounting to forty-six feet in a mile. But before 

 any inference of this kind can be accepted, some 

 considerations should be taken into account, of the 

 highest interest and importance in relation to the early 

 history both of the Campagna and of the Apennine 

 chain. 



Before dealing with these questions, however, let 

 us complete the examination of the marine deposits 

 of Monte Mario. In the valuable section disclosed 

 on the slopes of that hill, the grey clay is seen to 

 become sandy towards the top and to include seams 

 of sand which rapidly increase in thickness, until, with 

 their included layers of gravel, they form nearly the 

 whole of the upper part of the ridge. These yellow 

 sands, generally distinguished by the name of 'Astian,' 

 have been traced, like the clay below them, along 

 nearly the whole length of the Italian peninsula. The 



