HILL: GEOLOGY OF JAMAICA. ill 
truding 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 Rio Doro for five miles, be- 
tween Williamsfield, St. Catherine, and Newport, St. Mary. Usually 
these aro very weathered and so decomposed that they break down into fri- 
able rotten yellow and ferruginous débris, 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 Richmond, St. 
ary, 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 
‘bound in the same localities east of Clarendon, traversing the whole of 
the Blue Mountain Series.! In fact, wherever the rocks of this series 
“cur 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 
ften 300 feet or more thick. 
Tn Metcalfe the granitoids underlie and protrude into the conglomerates 
of the Minho beds. In the Plantain Garden region according to Barrett,? 
. 86 are immediately below the Hippurite bearing Cretaceous limestone ; 
a Portland, vide Barrett,’ south of Port Antonio, they underlie the same 
Imestone, which has been highly altered and metamorphosed along the 
Me 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 
t. Andrew they clearly protrude through the various rocks of the Blue 
9Untain Series.¿ South of Port Antonio they have apparently elevated 
A the rocks of the Blue Mountain Series and the Montpelier beds of the 
“eanic Series;* in St. Catherine they occur between the top of the 
lue 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. 808. 8 Ibid., p. 75, 
4 Ibid., p. 97, 5 Ibid., p. 106, 
* Ibid, p. 86. 
