90 THE WONDERS OF GEOLOGY. Lect. I. 



figure of an enormous frog ; it is of guaiacum, but has be- 

 come extremely hard, and as black as jet.* 



Human skeletons have also been found in solid calca- 

 reous tufa near Santa in Peru. Bones, belonging, it is 

 computed, to some scores of individuals, were discovered 

 imbedded in travertine, containing fragments of marine 

 shells which still possess colour. The bed of stone is 

 covered by a deep vegetable soil, and forms the face of a 

 hill crowned with brushwood and large trees, on the side of 

 the river Santa, f 



44. Isle of Ascension. — In the Isle of Ascension, 

 which is a volcanic cone in the midst of the Atlantic, 

 and appears to have been a dome of trachytic rocks, 

 subsequently affording vent to lava currents, a recent 

 deposit of conglomerate is going on. Its coasts are 

 flanked by accumulations of concreted sand with com- 

 minuted shells, corals, echini, and fragments of lava. The 

 specimens before us are portions of this modern rock 

 in various states of consolidation ; they are composed of 

 corals, which still retain their colour ; of shells, more or 

 less broken ; and of sand of similar materials ; they 

 also contain pebbles of trachytic and glassy lava. The 

 shores of this island are a favourite resort of turtles, which 

 repair thither in immense numbers, and deposit their eggs 

 in the loose sand : the rapid conversion of the coarse 

 calcareous banks into solid stone, occasions the frequent 

 imbedding and preservation of the eggs ; and there are 

 specimens in the cabinet of the Geological Society, in 

 which the bones of young turtles, just on the point of 



* In the former editions of this work a notice was given of some 

 supposed imprints of human feet on limestone, figured and described 

 in an early volume of the American Journal of Science. These mark- 

 ings have since been carefully examined by Dr. Dale Owen, of New 

 Harmony, and prove to have been sculptured by the Aborigines. 



f American Philosophical Transactions for 1828, p. 283. 



