270 



found near Arroyo Naranjo, Rincón, Saii Antonio de lo8 Bauos and 

 Gnira. In one of the younger portions of the Ynninri cleft-profile 

 feldspars were so numerous that they could i-eadily be examined in 

 the pulverized rock. All the splinters that were examined, had a 

 higher refractive index than canada balsam, so that there is a 

 complete lack of orthoclase and albite. Among 20 splinters examined 

 13 had a higher, 7 an equal or a lower refractive index than 

 eugenol (1 . 546), so the latter belong to oligoclase. Neaily all the 

 splinters have a lower refractive index than iiitrobenzol (1,556), so 

 that among the larger feldspar splinters, which are of course 

 fragments of phenociysts from the dacitic-andesitic rocks, from which 

 also the ground-mass originates, no plagioclases occur that are more 

 basic than andesine '). The etTusive rocks supplying the material for 

 submarine tuffs, must then have " been a highly acid, potassium- 

 poor dacite i.e., a rock in all points of the type of the "Pacific Rock". 

 It should be observed that the fragments of the ground-mass 

 occurring in the tuffs, very often have a diameter of 1 mm. It is 

 not out "of the bounds of possibility of course, that similar volcanic 

 material could have reached Cuba during an eruption of rather 

 remote volcanoes, if at the time of the eruption a violent storm had 

 been blowing in the direction of the island. The coarseness of the 

 fragments, however, together with the very high frequency of 

 volcanic material in formations extending from the eocene into the 

 pliocene in localities nearly 200 k.m. apart, indicate that this 

 material has not "come over" under "peculiar" circumstances from 

 far-away volcanic centra. These submarine volcanic tuffs that are 

 so widely diffused both stratigraphically and geographically, must 

 be regarded as evidence that in the Tertiary the volcanic activity 

 in the Antillean region extended over a much larger area than at 

 present and that it did not settle down before the close of the 

 Tertiary. This fact also tends to strengthen our view that the Antilles 

 are geologically homogeneous. 



It is likewise deserving of note, that no remains whatever are to 

 be found of the volcanoes that must have existed as late as the 

 latter half of the Tertiary in the neighbourhood of Cuba. This 

 proves that already since the beginning of the Tertiary Cuba must 

 have been subject to violent disturbances, where denudation destroyed 

 rapidly what had been built up by volcanic and orogenetic processes. 



1) The refractive indices of the fluids used in the Utrecht geological institute 

 for the determination of the refractive indices of minerals, have been verified only 

 a short time ago by Prof. Schoorl for which we tender our thanks. 



