28 TRANSACTIONS OF THE 



barrier to the spread of vegetation from the adjacent forest 

 or the transportation of material from the same source by 

 the wash of rains. The soil, thin as it is, probably con- 

 tained a very large share of the germs which have since de- 

 veloped ; while the wind, the birds and other animals have 

 lent their constant aid for what further was needed. At 

 the present time there is no vestige of this ancient work 

 save the moat, and looking at a like heavy growth of tim- 

 ber in a northern climate, no doubt would be entertained 

 that it was a forest of great age. 



Just in rear of the city of Cartagena, U. S. of Colombia, 

 there is a hill, some three hundred feet in elevation, sur- 

 mounted by a castle that was one of the principal defences 

 of the city less than half a century ago. The hillsides are 

 now completely and heavily overgrown with a matted tangle 

 of trees, vines, and parasites, so much so that a party at- 

 tempting in 1871 to climb the hill, were obliged, with no 

 little labor, to cut a pathway with the vigorous use of ma- 

 chetas, and were told by the inhabitants that no one had 

 attempted the ascent before for years. The castle, like the 

 city itself, with its fortified walls, its magnificent palaces, 

 churches, and convents, monuments of the skill, energy, and 

 lavish expenditure of the Spanish builders, is rapidly falling 

 into ruins, and is one of the many examples of the extremely 

 rapid progress in tropical America of the decay of the 

 strongest works, and heaviest masonry, when left without 

 proper care, especially exhibiting the heaving effect of 

 vegetable growth. Woodwork has two enemies — the rapid 

 alternation of moisture and burning sunshine, and boring in- 

 sects — the latter being almost as destructive as the teredo nav- 

 alis, though requiring a longer time for their work. The 

 present occupants of the land make little or no effort to arrest 

 the progress of destruction, and Porto Bello is almost as com- 

 plete a ruin as Pompeii, notwithstanding the very short time 

 that has elapsed since it was a wealthy and populous town. 



The rapid accumulation of strata in localities favorably 

 situated, and the growth of cottonwood groves on the banks 



