ART. VII.-A further Contribution to our knowledge of the Laurentian; by FRANK D. ADAMS. With Plates I and II.

THE chief of the great protaxes of the North American Continent, having an area of about two million square miles, lies as is well known for the most part in the Dominion of Canada, and in it Logan distinguished two great systems or series of rocks-the Huronian and the Laurentian-the former being a distinctly clastic series, while the latter showed no undoubted clastic structure but consisted chiefly of gneisses of various kinds. He also found associated with these Laurentian gneisses in certain parts of the protaxis an abundance of quartzite and crystalline limestone, as well as much anorthosite and eventually divided the Laurentian into two parts, viz: the Upper Laurentian-consisting of the anorthosites (supposed to be stratified rocks), with some of the gneiss and crystalline limestone, and the Lower Laurentian consisting of the Grenville series, distinguished by the presence of numerous bands of crystalline limestone, quartzite, etc., resting upon the Fundamental Gneiss.

These two divisions, the Upper and Lower, were supposed to be unconformable.

In a paper which appeared two years ago in the Neues Jahrbuch für Mineralogie,* under the title "Ueber das Norian oder Ober-Laurentian von Canada," it was shown from a study of all the areas of the so-called Upper Laurentian, that the rocks which had been assigned to it do not constitute an independent series, but that the anorthosites occur as a series of great intrusions, while the associated gneisses and crystalline limestones are merely portions of the Grenville Series or Fundamental Gneiss as the case may be.

In a paper which was recently presented to the Geological Society of America, moreover, Ells states it as his belief from a reëxamination of Logan's typical area that the crystalline limestones of the Grenville Series are not concentrated at some four widely separated horizons as Logan supposed, but come in gradually, as interstratified bands, attaining their principal development at the summit of the series.

It appears, therefore, that what has been called the Laurentian in Canada consists of an underlying series of gneisses and granites called the Fundamental Gneiss, much of which may be and probably is of igneous origin, and an overlying series of gneisses often differing from these in petrographical character, associated with crystalline limestones and quartzites, and known as the Grenville Series.

*Beilage Band, viii, 1893.

CLIFF COMPOSED OF WHITE GARNETIFEROUS QUARTZITE INTERBANDED WITH GARNETIFEROUS AND SILLIMANITE GNEISSES, NEARLY FLAT (LAURENTIAN). 2 MILES N. W. OF ST. JEAN DE MATHA, QUEBEC.