No abstract

Within the group of islands which together comprise Spitsbergen outcrops of dolerite may be traced over an area of about 50,000 square miles. The area is doubled if the neighbouring dolerites and basalts of Franz Josef Land are included. Even so, this is but a part of a network widely spread over the north-western part of the Euro-Asiatic continental platform, and over adjoining circumpolar lands. The sill-swarms of Spitsbergen alone rival in extent any of approximately similar age in other parts of the world, such as those of South Africa, South America, India, Antarctica, or North Britain. They merit a great deal more attention than it has yet been possible for geologists to devote to them.

The more or less flat-lying sedimentary rocks that build up the plateau country of the northern, central, and eastern parts of Spitsbergen range in age from Downtonian to Tertiary. The rocks with which it is proposed to deal in this paper constitute the basement underlying this sedimentary succession in the east central part of Spitsbergen, in the region at the head, and to the east, of Klaas Billen Bay, the north-eastern branch of the Ice Fiord (Map, fig. I). An extension of these basement rocks is to be found in the mountains east of Wijde Bay, and similar rocks are to be found in other parts of Spitsbergen, notably in the western mountain ranges. Formations up to the Tertiary, as well as the Pre-Devonian, are involved in the folding of these western ranges; but the rocks dealt with in this paper may be designated as older than the oldest unfolded rocks in the country.

No abstract

The lavas of the Scottish Carboniferous are predominantly basaltic. True andesites and rhyolites are conspicuous by their absence, whilst trachytes and allied rocks are present in quite subordinate quantity. This association of basalt and trachyte is in accordance with the fact that the basalts have a slight alkaline cast, which is evidenced by an alkali content greater than that of the average basalt, and by the occasional presence of nepheline and analcite amongst their constituents. The transition from basalts to more acid types is accomplished, not by way of the andesites, but through the mugearites, volcanic rocks with chemical affinities to the essexites. All transitions from the more felspathic types of basalts, the Jedburgh and Markle types, can be traced through mugearites to trachytes or allied rocks.