. Scientific survey of Porto Rico and the Virgin Islands. Scientific expeditions. 138 SCIENTIFIC SURVEY OF PORTO RICO The conglomerate is well shown north of La Lapa, where the Rio Cayev cuts a narrow gorge^, and again where the Jajome cuts through it west of Jajome bajo. The conglomerate phase is not dominant in all parts ol this series. In the eastern portion tuff occurs instead of the conglomerate and for this reason the Cayey-Ouayama Road between K. 15 and K. 21 shows comparatively few exposures of conglomerates. This transition from conglomerates to tuff is excellently shown along the tra
. Scientific survey of Porto Rico and the Virgin Islands. Scientific expeditions. 138 SCIENTIFIC SURVEY OF PORTO RICO The conglomerate is well shown north of La Lapa, where the Rio Cayev cuts a narrow gorge^, and again where the Jajome cuts through it west of Jajome bajo. The conglomerate phase is not dominant in all parts ol this series. In the eastern portion tuff occurs instead of the conglomerate and for this reason the Cayey-Ouayama Road between K. 15 and K. 21 shows comparatively few exposures of conglomerates. This transition from conglomerates to tuff is excellently shown along the trail, wliicli leads from K. 21 westward to Barrio del Carmen. STRUCTURE The synclinal structure found in the Barranquitas-Cayey series changes to anticlinal in the area of the rocks of the Sierra de Cayey series. Thus, O o ^o° o o ^-o? Fig. -Character of the unconformity hetiveen the Barranquitas-Cayey and the Sierm de Cayey series a fiat anticline exists between kilometer 15 and kilometer Going westward the strata begin to dip uniformly southward at angles between 30° and 40° and the strike varies between IST. 40° to 60° W. A break of importance occurs at the base of this series^ as indicated by the great conglomerate beds in the Sierra de Cayey group and by a distinct uncon- formity visible at two places. Thus between K. 86 and K. 87, on tlie Military Road west of Aibonito, the basal conglomerate of the Sierra de Cayey group rests upon the eroded surface of the underlying shales and contains pebbles of these shales (Fig. 8). Dips taken along this section show the shales to be gently folded and the conglomerate to lie upon tlie truncated portion of a faint anticlinal fold. Again, just west of where the Rio de Cuyon changes from a southward-flowing to an eastward-flo^v- ing stream, the heavy conglomerate lies upon a truncated portion of an anticlinal fold in the underlying shales. The upper contact is gradational with the overlying series. The formation is es
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