[The following is the text of a lecture delivered in Cambridge on 19 October 1978 to mark the 250th anniversary of the founding of the Woodwardian Chair.]

Studies on the distribution of manganese-bearing rocks in the Birimian and their relationship with gold mineralization are still in progress. Both manganese and gold occur as stratabound lenses within volcano-sedimentary sequence. Evidence of pre- and post-tectonic mineralizations are present. Sedimentological evidence also suggests both may have been contemporaneous with their host rocks in an environment that was strongly Eh and pH controlled. Under present tropical conditions, other elements associated with Birimian gold mineralization, notably copper and arsenic, are highly mobile to remain in residual soils. However, manganese, like iron, remains in residual soils as oxides and could be a useful pathfinder element in the search for gold in tropical lateritic soils derived from Precambrian greenstones.

Dionide hectori Reed, 1926, is shown on the basis of new collections from the type area in New Zealand to be a Tremadocian ceratopygide close to Hysterolenus. The species was placed in Taihungshania by Kobayashi (1941). It was provisionally retained in the Taihungshaniidae by Lu (1975) who made hectori type species of a new genus Hectoria (non Hectoria Trechmann, 1918). Ruapyge nom.nov. is proposed here for the reception of hectori. The original length/width ratio is determined by Wellman's method, with little consistency in results. Data from the strain ellipses constructed by Wellman's method are then used to calculate values for the attitude of the line of no finite longitudinal strain. The values obtained graphically do not agree with those derived from a formula given by Ramsay (1967); this contradictory situation is in need of explanation.

The Wagwater Belt is a fault-bounded structural unit in which more than 3000 m of early Tertiary sedimentary and volcanic rocks are exposed. Geochemical analyses of the volcanic rocks show that they comprise a bimodal suite of plateau-type tholeiitic basalts and calcalkaline dacites. The extrusion of these volcanics is associated with the development of an interarc basin, the Wagwater Basin, at the beginning of the Cenozoic Era. The Wagwater Basin formed as a result of the splitting of a mature late Cretaceous volcanic arc into a frontal and third arc represented by the Blue Mountain Massif and the Clarendon Block respectively. This model for Jamaica can be correlated with tectonic events occurring in the NW Caribbean during the early Tertiary. The creation of the Wagwater Basin and the eruption of the basalts is related to the initial opening of the Cayman Trough. The cessation of dacite volcanic activity in Jamaica signified the separation of the Caribbean Plate from the East Pacific Farallon Plate.

In reviewing those fossil algae associated with biotic reefs since the beginning of the Mesozoic, examples are discussed of algae showing evolution attributed to reef or peri-reefal conditions, those showing diversification attributed to reef environments, and those with frequent occurrence in reef conditions but with evolution not directly attributable to reefs.

Although the ammonoid Durvilleoceras is apparently very close in its morphology to early Triassic genera, it comes from a formation that underlies formations with early Triassic and late Permian faunas, and appears to be of late Middle Permian age. New occurrences of the ammonoid support this thesis. Conjecturally, the genus may have inhabited deep cold waters of the southern hemisphere during the Permian Period, before giving rise to genera found in shelf deposits of the early Triassic. Alternatively, if really Triassic in age, Durvilleoceras indicates a major low-angle thrust, previously unsuspected, that has repeated Triassic sequences for a length of over 450 km before disruption by the Alpine Fault. No evidence is yet known to support this alternative.

Major stratigraphical inversions are recognized in two parts of the Sulitjelma area, on the border of Norway and Sweden. In the Otervatn area, inversion is directly demonstrated by way-up structures in pillow lavas of the Sulitjelma Amphibolite Group. The porphyritic amphibolites of the group belong to a penecontemporaneous sheeted intrusive complex which originally underlay the pillow lavas. The other inversion, S of Sorjusjaure, is proposed in order to simplify the stratigraphical succession of the area. The inversions are both thought to belong to the inverted limb of the Gasak Nappe, which is the upper tectonic unit at Sulitjelma. Folding associated with the inversion could cause tectonic repetition of the strata-bound Sulitjelma ore horizon.