Dunean— Miocene Beds of Antigua and Malta. 99 
which is found in their line of strike, and in the position which 
a coral-reef would occupy in relation to its rocky basis. It is 
evident that the chert did not participate in the uptilting of the 
supporting strata, but that it was formed subsequently: it is 
equally clear that the chert and the inclined strata have 
suffered from oscillation of level and from great denudation. 
The marl, which was deposited during a period of subsidence, 
increased in thickness as the chert and the inclined strata sank 
slowly; and it is tolerably evident that, when the chert had 
passed considerably below the sea-level, the marl-forming reef 
was supported by the inclined strata. The marl is found 
above, beyond, and below the chert; it is in contact with the 
inclined strata; and it consists of the detritus of coral-reefs 
and of the remains of the Mollusca and Protozoa once living 
upon them. Its beds are imperfectly stratified, and are 
horizontal; its surface has been worn by denuding agencies, 
and its sea-margin supports recent coral-growths. It is of 
great depth; and its final upheaval was contemporaneous with 
that of the inclined strata and the chert. 
The history of these coralliferous strata would appear to be 
as follows:—-The trap and other igneous rocks, which now 
support the inclined calcareous strata, constituted the high land 
around which the first coral-atoll was formed; this, with its 
mud and detritus, gradually became, as the supporting rock 
subsided, a vast bed of calcareous marl and loam, coral-growth 
proceeding at the surface according to the usual laws. A 
period came when. the subsidence ceased, and then one of 
_ elevation commenced. ‘The coral-beds were tilted up, and the 
elevation which occurred in the restricted area of the original 
igneous rocks, did not affect the whole reef and mud equally: 
the part nearest the land was elevated, and the present dip of 
the inclined strata was determined. This elevation, which 
doubtlessly was gradual, was accompanied by voleanic outbursts, 
traces of which exist in and above the inclined strata. The 
inclined strata, together with the igneous rocks, then became 
surrounded by a coral-reef, of no very great luxuriance; and 
the whole gradually began to subside, until the future chert 
was developed from the coral-detritus, amongst which pieces 
of wood and brackish-water Testacea were mixed. The sub- 
sidence was over a larger area than the late upheaval, for the 
chert sank horizontally. The next change of level was an 
upheaval over as great an area as that of the subsidence; the 
chert was simply elevated with the mass of inclined strata and 
the old igneous rocks. It must have been lifted high above 
the sea, and doubtless frmged a hill-side, as the old reefs of 
H 2 
