UPPER CRETACEOUS. 641 



limestones and yellow clay. The rocks are usually of dark color (black, blue, or dull chocolate) , 

 in strong contrast to the glaringly light colors which characterize the succeeding formations 

 of the Oceanic and Coastal series. The material, with the exception of occasional' limestone 

 beds and a few outcrops of clay marls, can be traced to igneous rocks; it was first volcanic 

 ejecta and subsequently and successively underwent various degrees of attrition and sedi- 

 mentation from coarse bowlders and tuffs to finely triturated impure clay shale, a process 

 indicating extensive working over. These rocks are the material of the Central Mountains, 

 composing the eminences above 3,000 feet, such as the Blue Mountain Ridge. They undoubt- 

 edly underlie the surface rocks of the rest of the island, as occasionally revealed by erosion 

 through the white limestone which veneers them, as seen in some of the central basin valleys, 

 the canyons of the marginal streams, and certain bluffs of the back coast border along the 

 northwest coast. 



Nowhere on the island can all the beds of the series be seen in continuous exposure. As 

 has been noted concerning the rocks of the Blue Mountain district, "the strata are so excessively 

 disturbed, so traversed and semimetamorphosed by dikes of syenite and mixed up with porphy- 

 ritic masses, that it is impossible to observe the intricacies of the stratification or to determine 

 the sequence of the beds inter se without a lengthened and detailed investigation." Sufiicient 

 is known to state that it probably exceeds 5,000 feet. 



Previous attempts to classify the rocks which are collectively arranged in this series have 

 been confusing and unsatisfactory. * * * 



While it is still impossible completely to differentiate aU the beds of the Blue Mountain 

 series, our observations have enabled us to make a more accurate classification of them than 

 any hitherto presented, which may be stated as follows : 



Blue Mountain series: 



Upper division (Eocene) : Richmond beds. 

 Lower division (Upper Cretaceous) : 



Minho beds. 



Ballard beds. 



Logic Green beds. 



Frankenfield beds. 



Jerusalem beds. 



Yallahs beds. 



[In classifying the basement beds the chief difficulty] is the complex folding and partial 

 concealment which make it impossible to determine the exact base of the series. The Jamaican 

 reports present confficting conclusions on this subject, inconsistently stating in different places 

 that the base of the section is composed of igneous rocks, Cretaceous limestones, and a formation 

 termed the "Metamorphosed series." 



Hill quotes various opinions and states that the visible base of the section is 

 a great series of tuffs and conglomerates in which the fossiliferous Cretaceous beds 

 constitute local occurrences. The limestones are certainly the oldest rocks paleon- 

 tologically identifiable, but they are clearly intercalations in vast beds of igneous 

 debris. He searched w^ith care but in vain for evidence of some older or lower- 

 lying rocks bT:neath the Blue Mountain series. 



Referring to the lower division or Upper Cretaceous of the Blue Mountain 

 series, Hill says: 



AU beds of the lower subdivision, taken collectively, represent the product of disturbed 

 conditions^ such as active volcanism accompanied by the piliag up and contemporaneous 

 degradation of vast quantities of igneous material much of which was deposited below the sea 

 level, alternating with short periods of quiescence, when shales and marls were permitted to 

 accumulate and sparse faunas to gain temporary foothold. The alterations of shale and igneous 

 material in the Blue Mountain series indicate alternating conditions of sedimental placidity 

 48011°— 12 41 



