On the western and eastern sides of the North Atlantic craton, rocks between about 1·7 b.y. and 1·2 b.y. old are represented by thick basinal assemblages. Thin platformal successions cover the intervening region. The clastic component of these rocks was largely derived from the southeast where the Elsonian orogen might have been an important source terrane. Widespread mafic igneous activity (about 1·2 b.y. ago) in the central platformal region preceded orogenic movements in the basinal areas (Racklan-Carolinidian-Grenville orogeny). The Grenville orogen may have contributed significant amounts of clastic debris for a second cycle of sedimentary accumulation(∼ 1·2 b.y.–∼ 0·8 b.y.). The upper part of this cycle typically contains red beds and evaporites and, in the North American Cordillera, shows evidence of contemporaneous block faulting and extensional tectonism. These movements culminated in the East Kootenay and Hayhook orogenies and ushered in a third period of deposition about 850 m.y. ago. The third sequence includes glaciogenic rocks in the Cordilleran and East Greenland geosynclines. The basic geotectonic elements (platforms and geosynclines) of the North Atlantic craton were established as much as 1·7 b.y. ago, but continental fragmentation on the borders of the craton may not have taken place until early Phanerozoic times.

The structure of the fishes constituting the Devonian genus Cheirolepis is investigated. Articulated remains from the Scottish Old Red Sandstone and the Canadian Upper Devonian were studied and two species are recognised, the Middle Devonian C. trailli and the Upper Devonian C. canadensis. Recently described fragmentary material from Europe assigned to the genus is best regarded as incertae sedis. Cheirolepis is the earliest actinopterygian genus with extensive material. Neurocranial remains are described, with a crossopterygian-like parasphenoid. There seems to have been a mobile rostral region with several small bones between premaxilla and postrostral extending to the anterior corner of the small dermal orbit. New palatoquadrate and pectoral girdle material is described. The apparently primitive nature of the head skeleton is related to the cranial dynamics and the likely mode of life. The small scales and the elongate-fusiform body shape are a corollary of the method of swimming. The ecology of the fishes is touched upon. A taxonomic investigation of the two species was carried out but although interesting variation in the scale-row numbers came to light no changes at the specific level were deemed necessary. Revised generic and specific diagnoses are given.