600 Dr. J. W. Spencer — The Tumuri Valley of Cuba. 



of the tributary valleys t&^lhe foot of Pan de Matanzas, as shown on 

 Map (Fig. 1). The floor of the basin rises from near tide-level to 

 considerable elevations in its upper part, where there are low ridges 

 produced by the unequal washings of the tropical rains. The floor 

 of the lower part of the basin has been silted up so as to be 





% 1 

 Fig. 1. Map of the Tumuri Valley, A B, position of section shown in Fig. 3. 



level, and it is bounded by steep wave-washed banks indicating its 

 former lacustrine character. The floor of the basin is underlaid by 

 Cretaceous sands, decaying serpentine rock, or Tertiary limestone, 

 which have been very extensively removed so as to expose the other 

 and older named beds. The original valley was excavated out of 

 the upturned beds of Miocene and Eocene limestones. During the 

 following submergence, at the close of the Pliocene period, the 

 valley does not appear to have been completely filled with the later 

 calcareous rocks (Matanzas limestone of the author '), which contain, 

 mostly, living organisms. During the long epoch of the earlier 

 Pleistocene elevation and erosion, the Yumuri Yalley was again 

 excavated, and in some parts enlarged, so that only fragments of 

 the Matanzas limestones are found on the sides of the valley. The 

 south-eastern end of the basin is about three miles wide, and is 

 divided by a hill into two lobes. The basin is cut off from the bay 

 (or rather fjord) of Matanzas (with an increasing depth of from 

 1000 to 1500 feet) by a barrier ridge, whose base is about a mile 

 wide, and whose height is from 250 to over 450 feet above tide 

 (see Fig. 3). The Miocene and Eocene strata dip at from 20° to 

 30° S. 20° E., whilst the overlying Matanzas marls dip at 10° or 

 12° N. 20° E. ; and these last are succeeded by modern coral-reefs 

 on the seaward side of the ridge. The outlet of the broad valley is 

 a canon with vertical walls (below and sloping above) rising 250 feet 

 above the water, and with a breadth of only 300 feet, like many other 



^ Described in a paper read before the Brookljni Meeting of Am. Assoc. Ad. So. 

 as an advanced notice of an unfinished paper. ' 



