76 J. W. SPENCER — GEOGRAPHICAL EVOLUTION OF CUBA. 



rated into the Eocene and Miocene systems, they constitute, however, a 

 ph3^sical unit, apparently witliout important stratigraphic breaks. 



Matanzas region. — Between Havana and Matanzas the Tertiary lime- 

 stones form prominent ridges surmounting a country which is from 300 to 

 400 feet above the sea. These ridges are commonly low and interrupted, 

 but at a point about 10 miles west of Matanzas they are rendered conspic- 

 uous by two butte-like masses, of which Pan de Matanzas, rising to 1,277 

 feet above the sea, is the higher (see figure 7, page 87). Eastward of the 

 Pan the ridges become lower, but appear to rest upon the margin of an 

 old baselevel plain of about 400 feet altitude, out of which the Vale de 

 Yumuri is excavated. At Matanzas the Yumuri river has recently cut a 

 canyon across the ridge and exposed the best section of Tertiary forma- 

 tions the writer has seen in Cuba. It is shown in figure 4. The section 



Figure 4. — Section along Yumuri Canyon. 



S=sealevel; E-C= raised modern coral reef; iW= Matanzas (Pliocene?) limestones resting 

 nnconformably upon the Miocene ; B = undulations in mechanical beds ; D = base (?) of the 

 Miocene ; A = undulations in Eocene beds ; F= fault-beds shown in their natural dip. 



The length of the section is 3,800 feet in a direction at right angles to the strike. 



extends from the church near the mouth of the river along the gorge to 

 the Yumuri valley. The canyon is only about 300 feet wide, and the 

 walls reach an elevation of about 250 feet at a short distance from the 

 river. This canyon will be explained later. 



From the fault near the northwestern end of the gorge the valley opens 

 out, and accordingly the lower Tertiary beds are lacking, through re- 

 moval, on the northern side of the gorge, but upon the southern side of 

 the valley they are further exposed for half a mile or more. The dip 

 at the southeastern end of the section, in what have been called by the 

 author Matanzas limestones, is 13° to 15° north, 10° to 20° east. The upper 

 beds of the underl3dng and unconformable Miocene strata dip 30° south, 

 30° eaot, but this inclination is reduced in the lower beds to from 20° 

 to 25°. At the fault near the inner end of the gorge the adjacent beds, 

 dipping at 60°, show dislocation, but beyond the location of the fault the 

 dip of the beds becomes normal. Reduced to vertical measurement, the 

 formation shows the following section: 



Pliocene (?) (Matanzas) : Feet 

 White and creamy earthy fossiliferous limestones with some calcare- 

 ous pebbles and fragments 150 



