176 THE VOYAGE OF H.M.8. CHALLENGER. 



Radiolarians and siliceous Sponge spicules. In some instances the pumice stones were 

 completely coated with Serpula, Polytrema, and calcareous Algse. 



The ship passed between Pico and San Jorge, and on the 3rd obtained a dredging in 

 900 fathoms between Pico and San Miguel. The bottom was a Pteropod ooze, con- 

 taining 52 per cent, of carbonate of lime, which consisted of Pteropods, Hetcropods, 

 Foraminifera, Coccoliths, Rhabdoliths, and fragments of Molluscs and Echinoderms. The 

 mineral particles were all of volcanic origin. The dredge contained a few Echinoderms, 

 Annelids, Polyzoa, Hydrozoa, and Crustaceans. 



It was noticed, during the time the ship was kept stationary, that the surface water 

 ran to the westward in the forenoon and to the eastward in the afternoon. Now, on the 

 3rd it was high water at Fayal at 5.30 p.m., and consequently low water at 11.30 A.M., 

 from which it would appear that the flood tide sets to the eastward and the ebb to the 

 westward in the vicinity of the Azores. 



On the 4th, at 6.40 p.m., the Challenger arrived at Ponta Delgada, the chief town 

 of the island of San Miguel, and, there being no epidemic, remained there five days. 



During the stay at San Miguel excursions were made to many parts of the island, but 

 more especially to the Caldeira des Sette Cidades, or Cauldron of the Seven Cities, situ- 

 ated at the western, and the picturesque valley of the Furnas at the eastern, end of the 

 island. The former is a marvellous hollow of enormous size, with two lakes at its bottom 

 and a number of villages in it. One slowly climbs the mountains from the sea and 

 suddenly looks down from the edge upon the lakes, 1500 feet below. On the flat 

 bottom of the main crater, which is covered with verdure and cultivated fields, are several 

 small secondary cones, the whole reminding one of the representation of a lunar volcano. 

 One of the small craters has been so cut up by deep water-courses, that between them 

 only a series of sharp radiating ridges is left standing, and it thus presents a very 

 fantastic appearance. 



The Furnas valley is a similar deep, nearly circular crater, in which there is 

 a large lake, numerous boiling springs, and the Furnas village, — the fashionable 

 watering place of San Miguel. Sir Wyville Thomson writes : — " The principal 

 boiling springs are about half a mile from the village. Round them, over an 

 area of perhaps a quarter of a mile square, there are scorched-looking heaps 

 like those which one sees about an iron-work, only whitish usually, and often 

 yellow from an incrustation of sulphur. Over the ground, among one's feet, little 

 pools of water collect everywhere, and these are all boiling briskly. This boiling 

 is due, however, chiefly to the escape of carbonic acid, and of vapour formed below, 

 for the temperature, even of the hottest springs, does not seem to rise above 

 90° C. The largest of the springs is a well about twelve feet in diameter, enclosed 

 within a circular wall. The water hisses up in a wide column nearly at the boiling 

 point, bubbling in the centre to a height of a couple of feet, and sending up columns 



