A. M. Finlayson—Petrology of Huelva, Spain. 227 
shearing seen in the porphyries, and the epidotization ‘of the adjoining 
slates is subsequent to the sericitization of the slates which accompanied 
the development of cleavage throughout the area. The basic rocks 
must therefore have been intruded towards the end of the series of 
movements which has affected the district, and a considerable time- 
interval has clearly separated them from the older granites and 
porphyries. 7 
STRUCTURE. 
The slates of the area show a very uniform east-and-west strike, 
while the dip is generally to the north at a varying angle. This 
alignment is preserved in the associated igneous rocks. In the absence 
of folding or of overthrusting, there would be a very great thickness 
of rocks to account for between the coastal district and the northern 
metamorphic complex. In the absence of fossiliferous horizons, or of 
strata with a persistent lithological character, the structure of the 
district is difficult to unravel. The observed facts, however, suggest 
the presence of a series of inclined isoclinal folds, which have been 
followed, further, by overthrusting along the limbs of the folds, more 
especially in the neighbourhood of the junctions of porphyry and slate. 
These junctions have clearly in many cases been lines of movement, as 
indicated by the marginal phases of cleaved and brecciated porphyry. 
Further, the lode-zones also invariably occupy lines of structural 
weakness. Thus many lodes occur at the junction of slate and 
porphyry, some at the junction of slate and diabase, and the majority 
are contained in belts of crushed or sheared slate, enclosed between 
more resistent sills of porphyry or bands of greywacke or quartzite. 
The persistent lenticular form of the lodes also indicates that they 
occupy zones of fault-sipping. The shearing and faulting along the 
present lode-zones was, however, distinctly later than the folding 
of the rocks and the development of cleavage in them, since it involves 
the basic intrusions, and since breccias along the lode-walls, cemented 
by ore, are seen to contain fragments of previously cleaved and 
sericitized slate and porphyry. These thrust-movements, which 
preceded the deposition of the ores, were, therefore, the last of the 
series of Hercynian disturbances in the district. sae al 
ConcLUsIONS. 
The general sequence of events in the area during the Hercynian 
epoch of crust-movement appears to have been as follows: -The 
deposition of the Lower Carboniferous strata was succeeded by elevation 
and folding of the rocks, the forces acting along north and south lines, 
probably towards the north. With the inception of pressure came 
intrusions of granitic and porphyritic rocks, varying from acid to 
intermediate, throughout the stressed area. Further pressure after 
these intrusions resulted in cleavage of the slates and considerable 
dynamic alteration of the porphyries, especially along their margins, 
where they offered least resistance. After an interval of rest there 
was a renewal of sub-crustal forces, expressed first by the intrusion of 
basic rocks over the same area, and then by further pressure which 
resulted in shearing and probably overthrusting along zones of 
weakness. The deposition of the ores immediately followed these last 
