58 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
In places the Richmond beds grade up into irregular alternations of 
impure clay, marls, and yellow limestones, which, in general, occupy a 
transitional position between the obviously land derived beds of the 
Blue Mountain Series and the ocean derived limestones of the Oceanic 
Series. Argillaceous calcareous marls appear in the upper part of the 
Richmond beds, become successively more and more frequent, and 
finally dominate, These are accompanied by thin beds of impure blue 
limestone of a segregational character, oxidizing yellow on weathering 
and alternating with the marls which gradually increase in thickness 
and relative proportion until they preponderate. Finally, these yellow 
limestones become more purely calcareous in ascending series as the 
sediments become clearer and freer from land derived material, until 
they finally pass into the purer White limestones. 
This formation has limited exposures at many places in the island, 
notably around the lower margins of the interior basins in Trelawney, 
Westmoreland, and Clarendon, and in the eastern parishes, as men- 
tioned later. We shall first describe their occurrence in two typical 
localities at Catadupa near Cambridge, and at Chapelton, Clarendon 
Parish, respectively. Owing to certain differences which at present do 
not permit of perfect correlation, these will be respectively termed the 
Jatadupa and Chapelton beds of the Cambridge Formation. 
The Catadupa Beds. 
. They are well exposed on the east margin of Great River valley, in 
the new cuttings along the Montego Bay Railroad between Ipswich and 
Montpelier stations, and especially between points two or three miles 
south of Catadupa and one mile north of Cambridge. Here the railway 
cuttings reveal splendid exposures, and afford good places for collecting 
fossils and studying the stratigraphy. These beds occur in a series of 
short open folds, as shown in Figure 20. 
These folds are all less than two hundred yards in length, but the 
continuity of the beds is so broken that their exact sequence and thick- 
ness can be made out only with difficulty. Here the beds consist of 
alternations of massive and friable strata of yellow blue limestone, one 
to three feet in thickness, separated by thin bands of blue-black shale 
containing oysters, large Cerithii, Lucina, Rudistes, Carolia, Triloculina, 
etc. 
A general geological section of the east slope of the valley of Great 
River, between Cambridge and Catadupa, showing the relations of the 
formation, is as follows. 
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