MUSEUM OF COMPARATIVE ZOOLOGY. 195 



ful cultivation a large plantation producing sugar, coffee, and all the 

 tropical fruits, as well as extensive tracts on which his herds of cattle, 

 sheep, and donkeys roam towards the higher central parts of the island, 

 show the fertility of these islands. They are indeed as favorably situ- 

 ated for cultivation as the Sandwich Islands or Mauritius, and there is 

 no reason why, if property managed, they should not in the near future 

 yield to their owners as large returns as do those islands. 



I obtained from Mr. Cobos a piece of the so called sandstone said to 

 occur on Indefatigable Island, and which of course I was most anxious to 

 see, as the occurrence of true sandstone would have put quite a ditferent 

 face on the geological history of the Galapagos from the one usually re- 

 ceived. This I found to be nothing but coral rock limestone, either a 

 breccia or slightly oolitic, identical with the formation found back of the 

 beach at Wreck Bay on Chatham Island. 1 found there an old coral 

 rock beach, extending on the flat behind the present beach, composed 

 entirely of fragments of corals, of mollusks, and other invertebrates, 

 cemented together into a moderately compact oolitic limestone, which 

 when discolored, as it often is and turned gray, would readily be mistaken 

 for sandstone. This coral rock is covered by j ust such a thin, ringing 

 coating of limestone as characterizes the modern reef rock of other local- 

 ities. On nearly all the islands there are a number of sandy beaches 

 made up of decomposed fragments of corals and other invertebrates, and 

 cemented together at or beyond high-water mark into the modern reef 

 rock I have described. The coral is mainly made up of fragments of 

 Pocillopora, which is found covering more or less extensive patches off 

 these coral sand beaches, but which, as is well known, never forms true 

 coral reef in the Panamic district. The only true coral reef belonging to 

 this district is that of Clipperton Island, (if we can trust the Admiralty 

 charts,) situated about 700 miles to the southwest of Acapulco. But 

 neither at Cocos Island, nor at the Galapagos, nor anywhere in the Pana- 

 mic district, do we find true coral reefs, — nothing but isolated patches 

 of reef-building coral. The absence of coral reefs in this district has of 

 course already been noted by other naturalists, who have been struck by 

 this feature in an equatorial region. Dana has ascribed it to the lower 

 temperature of the water due to the action of the Humboldt Current com- 

 ing from the south, pouring into the Bay of Panama, and then flowing 

 westward with the colder northerly current coming down the west coast 

 of Mexico and Central America. From the investigations made this year 

 by the " x\lbatross," I am more inclined to assume that the true cause 

 of the absence of coral reefs on the west coast of Central America is due 



