hill: geology of Jamaica. Ill 



trading into the overlying rocks, which clearly show their subsequent 

 origin." 



Splendid exposures of hornblende diorites are seen along the highway 

 and railroad as they follow the valley of the Kio Doro for five miles, be- 

 tween Williamsfield, St. Catherine, and Newport, St. Mary. Usually 

 these are very weathered and so decomposed that they break down into fri- 

 able rotten yellow and ferruginous debris, which is cut away with spades 

 by the road makers, but maintains a porphyritic structure to the last. Just 

 north of the new iron bridge the railway cuttings exhibit for the first 

 time exposures of the material in a fresh and comparatively unaltered 

 state, specimens of which are the basis of Cross's description. This ma- 

 terial everywhere has a vertical arrangement, as if it had been thrust up 

 from below. On the south side of the area in St. Catherine it is overlain 

 by the Cambridge formation, while to the north near Kichmond, St. 

 Mary, it is covered by the Richmond beds. 



The intrusive nature of these rocks, both dioritic and granitoid, is 

 seen everywhere throughout the districts mentioned. The dioritic dikes 

 abound in the same localities east of Clarendon, traversing the whole of 

 the Blue Mountain Series.^ In fact, wherever the rocks of this series 

 occur east of Clarendon, the intrusions can be seen pushed through the 

 strata and altering the adjacent rocks. But few of these dikes are of 

 narrow even sided proportions, but are mostly broad and ragged, and 

 often 300 feet or more thick. 



In Metcalfe the granitoids underlie and protrude into the conglomerates 

 of the Minho beds. In the Plantain Garden region according to Barrett,^ 

 these are immediately below the Hippurite bearing Cretaceous limestone ; 

 in Portland, vide Barrett,^ south of Port Antonio, they underlie the same 

 limestone, which has been highly altered and metamorphosed along the 

 line of contact. Between Guava Ridge and Content they have pushed 

 up into the shale beds of the Blue Mountain Series,* as seen by us ; in 

 St. Andrew they clearly protrude through the various rocks of the Blue 

 Mountain Series.^ South of Port Antonio they have apparently elevated 

 all the rocks of the Blue Mountain Series and the Montpelier beds of the 

 Oceanic Series;' in St. Catherine they occur between the top of the 

 Blue Mountain conglomerates and the base of the white limestones, 

 and abut against and metamorphose the latter in the northeast corner 



1 Jamaican Reports, pp. 65, 71, 93, 95, 112, 122, 144, 188. 



2 Ibid., p. 308. 8 Ibid., p. 75. 

 * Ibid., p. 97. 5 Ibid., p. 106. 

 6 Ibid., p. 86. 



