338 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VOL. V. 



The Layton For)]iation. — After the long Mio-Pliocene elevation, 

 Jamaica sank to about 500 feet below sea level, accordingly up to that 

 elevation, a newer series of beds is now found. These rest uncon- 

 formably upon the eroded surfaces of the " White Limestones ; " but 

 as they form only fringes about the high plateaus, and have been very 

 greatly denuded, they occur only in isolated fragments where protected 

 in some embayment of older date. A well-preserved fragment may be 

 taken as an example of the formation. 



Between Hope Bay and Great Spanish River there are the remains 

 of the Low Layton volcano (see Map, Figure 6. page 345), which is 

 called the Black Hill, rising to an altitude of 700 feet, which dates back 

 to the Pliocene period, but considerably anterior to the formation 

 of the marls which lie upon its denuded surface. This hill has pro- 

 tected the marls more or less against the marine erosion upon the sides 

 of the sea. Just after crossing Swift River, which enters Hope Bay, 

 some dislocated beds of shale are seen along the roadside, appearing 

 from beneath the base of the " White Limestones," whose beds are 

 always more or less distorted. On the eroded surfaces of the limestone 

 there occurs a heavy deposit of marls, in colour from white to yellowish, 

 or nearer the old volcano of gray tint, on account of the inclusion of 

 volcanic ashes. The western end of the volcano is shown in Fig. i, Plate 

 HL The beds are laminated and are not seen to undulate with a dip 

 of more than seven degrees, but as a whole, the formation may be con- 

 sidered as horizontal. The laminations are distinct in places, while in 

 others they are represented by lines of pebbles or rounded gravel com- 

 monly not more than three inches long, but the pebbles may be double 

 that length. These are composed of white limestones which form the 

 adjacent coast range, or nearer the volcano, some of the pebbles are 

 water-worn volcanic bombs or other fragments. Scattered through the 

 marls, there are blocks of white limestones, sometimes having a size of 

 from ten to twenty cubic feet, in part derived from the adjacent moun- 

 tain, and in part from the volcano. These large blocks are dependent 

 upon local conditions, but it is of primary importance to note that the 

 marl is largely a mechanical accumulation, derived from the degrada- 

 tion of the white limestones. The formation rises to an elevation of 

 about 475 feet above the adjacent Honduras sea, but its maximum 

 thickness cannot be specified as it rests unconformably on the " White 

 Limestones," and its own surface was subsequently greatly denuded ; 

 and afterwards succeeded by a minor formation. 



This locality may be considered as a typical remnant of the forma- 



