Guppy Reprint 



139 



in a shallower sea than the true oceanic beds and one wherein the 

 conditions varied somewhat from those. 



During the cretaceous period the Amazonian and Orinocan 

 region was occupied by sea as shown by Karsten (Geognostiche 

 Verhaltnisse des westlichen Columbien), while at the same time 

 a portion of the Atlantic Ocean was occupied by land. As ex- 

 plained in my papers ("Growth of Trinidad" and "Geological 

 Connexions of the Caribean Region,") the sediments of which 

 the rocks of Trinidad are composed were up to the end of the cre- 

 taceous period derived from the land which existed to the north 

 and north-east. But upon the close of the cretaceous period and 

 the gradual rise and filling up of the Amazonian and Orinocan 

 region, the sediments now came from the west and south-west 

 inaugurating the period of asphaltic and carbonaceous deposits 

 which probably continued throughout the tertiary period. 



The origin of the carbonaceous substances is to be found in 

 the vast quantities of vegetable matter brought down by the 

 rivers from the continent of South America. This matter being 

 of a slightly greater specific gravity than water, is subject to the 

 laws which govern the removal and deposition of sediment or 

 clastic material. Now one of these laws is that material of like 

 specific gravity and of like fineness or coarseness of grain or di- 

 mensions of the component parts is deposited together and apart 

 from dissimilar materials. Hence the vegetable matter brought 

 down by the rivers was deposited in layers banks or strata be- 

 coming interstratified with other sedimentary materials as the 

 process of sedimentation and deposition went on. Chemical 

 changes supervened which converted the vegetable tissues into 

 the forms in which we now find them, namely Lignite, Asphalt, 

 Manjak and Petroleum. 



P. S. — Basing my opinion on the theory expounded above, 

 I predicted two or three years ago that petroleum would be found 

 in the deltas or sedimentary formations at the mouths of tropical 

 rivers. The prediction has already been verified in the cases of 

 Nigeria and Tampico. 



