284 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



How are the harbors to be explained? Doctor Hayes and I 

 believed we found the answer in the conditions at present existing 

 along Yumuri River, near Matanzas. The river here empties into 

 the sea through a narrow gorge cut through Miocene limestone and 

 marls (see pi. 71, fig. C). The top of the gorge is 200 feet above 

 sea level, while farther back from the stream altitudes of 400 feet 

 or slightly more are attained. Above the gorge, the Yumuri and 

 its tributary, Rio Caico, have sunk their courses through the lime- 

 stone, have removed it, and have developed wide, almost base-level 

 valleys (see pi. 71, fig. D), on the underlying softer sandstone 

 and shale. If this basin were depressed sufficiently to let the sea 

 into it through Yumuri gorge a pouch-shaped harbor would result. 



Additional evidence bearing on the problem of the origin of these 

 harbors was obtained from records of borings. Mr. C. A. Knowlton, 

 an engineer at Santiago, reported to us that in boring wells in the 

 valley of San Juan River, 3 miles southeast of Santiago, he found 

 at a depth of 70 feet below sea level what appeared to be stream 

 gravel. Even more convincing evidence was obtained in Habana 

 Harbor. In the preparation of plans for a sewerage system the 

 Military Governor had a series of borings made across the harbor. 

 This harbor occurs in a rather wide valley surrounded by sides 

 which slope upward from sea level to an altitude of about 200 feet. 

 The borings revealed a submerged terraced valley within the wider 

 valley and in the middle of the inner valley a channel reaching a 

 depth of more than 30 meters (about 100 feet) below sea level (see 

 text-fig. 14). The depth of the first flat above the sides of the 

 channel is about 13 meters (about 42 feet) below sea level. This flat 

 is now covered with sand and the submerged channel is filled with 

 sand and clay. There are at present no known processes whereby 

 such a channel and terrace could be developed and then buried, 

 except by a higher stand of the land enabling a stream to cut a 

 trench and develop a terrace, followed by a lower stand of the land 

 which submerged both the channel and the terrace and resulted in 

 their burial by sediment deposited over them. 



It appears to me that there is no escape from the interpretation, 

 made first by Crosby, that the pouch-shaped harbors are drowned 

 drainage basins. Before the accumulation of the data by Hayes, 

 Spencer, and me, Hill endeavored to explain them without a shift 

 in height of strand-line, but after the additional information was 

 presented to him he abandoned his interpretation and accepted ours. 

 There is a statement to this effect in a manuscript by him now in my 

 possession, and this citation is made with his authority. 



The factors producing the peculiar form of the harbors will now 

 be briefly considered. According to Crosby, Hill, and the account 

 in our report on Cuba, fringing reefs are supposed to have restricted 



