260 BULLETIN 103, UNITED STATES NATIONAL MUSEUM. 



gravel and cobbles overlie the surface of the bedded tuffs at a number 

 of places, two of which are Casada Gardens and Gunthorpe sugar- 

 factory. At Morris Looby Hill, near the head of Willoughby Bay, 

 conglomerate immediately underlies the limestone; and the basal 

 contact of the formation is also exposed on the north side of Wil- 

 loughby Bay, where it is underlain by conglomerate, mostly composed 

 of basic volcanic material. The main reef occurs within the Antigua 

 formation at or near its base and is exposed along a southwest- 

 northeast line from Willoughby Bay to near Wetherell Point. The 

 Antigua reef therefore grew upon a basement that had been sub- 

 aerially eroded and was later depressed below sea level. The reef 

 and the limestone of which the reef forms a part were formed during 

 or after the submergence of their basement. Associated with the 

 corals are many specimens of several species of Lepidocyclina, which 

 are organisms characteristic of shallow, tropical water. The area! 

 extent of these sediments, coupled with the fact that the deformation 

 of the water-bedded tuffs that lie below the Antigua formation is not 

 much greater than that of the Antigua formation, indicates that 

 they were deposited on a submarine flat. In the northeastern part 

 of the island both the tuffs and the limestone, according to J. W. 

 Spencer, dip northeastward at a rate of 12° to 20 °. 1 My own meas- 

 urements show dips of about 20° toward the north or northeast for 

 the volcanic tuffs and dips between 10° and 15° in amount, and rang- 

 ing from N. 60° E. to N. 70° E. in direction, for the Antigua formation. 

 The rocks are more disturbed in the Central Plain, where the dips 

 of the volcanic tuffs were measured. Therefore, according to the 

 available evidence the Antigua formation was a relatively extensive 

 formation deposited in shoal water on a flattish floor. 



The main reef-coral bed is about 60 feet thick and is near the 

 bottom of the formation. Above it corals are scarcer, but appear 

 to be too sparingly distributed throughout a thickness of about 300 

 feet of limestone above their profuse development nearer the base, 

 or the Antigua formation seems to have a total thickness of a little 

 more than 350 feet. 



PORTO RICO. 



The middle Oligocene coral fauna, as has been stated on page 204, 

 occurs in the geologic formation to which Hill applied the name 

 Pepino. This is a hard, calcareous marl, full of coral heads, with 

 occasional indurated strata of white porous limestone. It is well 

 exposed north and northwest of Lares in the Pepino Hills, whence 

 the name for the formation is derived and where the collection of 

 corals submitted to me by Mr. Hill was obtained. 2 This is the for- 



1 Spencer, J. W., On the geological and physical development of Antigua, Geo). Soc. London Quart. 

 Journ., vol. 57, pp. 494, 496, 1901. 



2 Hill, R. T., Notes on the forest conditions of Porto Rico, U S. Department of Agriculture, Div. of 

 Forestry Bull. No. 25, pp. 14, 15, 1899. 



