The Genesis of the Gold-Deposits of Barkerville (British Columbia) and the Vicinity

Abstract

I. INTRODUCTION. The characters of the basic sills of Caernarvonshire have been described in detail by several writers, notably by Mr. ttarker in his well-known essay on the Bala Volcanic Series. There is a marked absence of dykes in association with the outbursts of this period, and the numerous basic dykes of this area have generally been assigned to a later series of eruptions. The evidence upon which this assumption rests is, however, not always satisfactory; and although Mr. Harker is inclined to favour their post-Carboniferous age, he does not conceal the uncertainty of this conclusion in several eases, and he adduces evidence which seems to point, at least in some instances, to the possibility of the existence of more than one group of these intrusions. Dr. C. A Matley, also, finds that in Northern Anglesey at least two groups of dykes occur, of which the earlier are pre-Silurian and the later post-Ordovician But Mr. E. Greenly maintains that the later dykes of Anglesey, including those of the Menai Straits, are certainly post-Carboniferous, and may possibly be evea of Tertiary age. With regard to the Llyn-Padarn dykes, with which this paper is ciliefly concerned, no very detailed description appears to have been published, although several authors have incidentally referred to them, as will be mentioned hereafter. It appears to have been generally assumed that these dykes are of the same age as those of the Menai Straits, to which they are supposed to bear a general resemblance, both, in petrographical