^{page 159 note 1} Geology of Ireland, p. 175.

^{page 160 note 1} Ibid, Chapter x. page 175.

^{page 160 note 2} In the old world the terms Lower Silurian, Upper Silurian, Devonian and Lower Old Ked Sandstone are used so indiscriminately that it is hard to know exactly what rocks are meant. In this paper Selwyn will be followed and to indicate Lower Silurians Phillips's term Cambro-Silurian will be used, while all the others will be included under the term Devono-Silurian.

^{page 160 note 3} In connection with this metamorphism of adjoining rocks, it may be mentioned that in the BelYoir section (Cambro-Silurian), Co. Clare, there are some beds in the fossiliferous strata altered apparently for no particular reason.

^{page 162 note 1} Geol. Mag. 1871, Vol. VIII. pp. 263–268.Google Scholar

^{page 162 note 2} Geology of Ireland, chapter x.

^{page 163 note 1} It appears remarkable that metamorphism seems to be so restricted to the older rocks in Canada. Is it possible, that in the areas called Archæan, from their lithological character, there may be newer rocks included? If not, why should metamorphism be so confined to them, when in a little spot like Ireland we have metamorphosed Cambrians, Cambro-Silurians, Devono-Silurians, Carboniferous (?) and Lias.

^{page 163 note 2} Excessive metamorphic action in a portion of an area will change rocks into granite; but if a milder metamorphism invades rocks at different successive times, it ought to more and more develope the plates or leaves without obliterating them. This can be seen on a small scale in different places in Ireland, the best perhaps being along the before-mentioned boundary of the older, or “ Slieve Croob” granite of the Mourne Mountain district. In general in Irish localities the additional metamorphism seems due to Metapepsis, succeeding Paroptesis, orvice versâ; but in some places one period of Metapepsis seems to have been followed by another. As the Canadian rocks are so ancient, we may suppose that at least three or four times they have been covered by a sufficient depth of strata to develope metamorphic action, but not sufficient to convert them into typical granite. It appears to me an interesting problem, why in such vast areas we should have gneiss without its being, in part, converted into granite of metamorphic origin? Unless we suppose that some of the rocks that are now gneiss were at one time granite, but by subsequent metamorphic action foliation was developed in it, and thus by degrees it was changed into gneiss. Such a change can take place; because if the “ Slieve Croob granite” we covered up with a sufficient depth of strata, it would be entirely converted into gneiss.

^{page 163 note 3} Mixed up, either as strata or small intrusions, with these rocks of Wexford, Galway, and Mayo, are eruptive rocks; they, however, were portions of the geological groups (Cambrians and Cambro-Silurians) and not subsequent intrusions, as was the case in respect to the Castlebar district porphyritic gneiss.

^{page 165 note 1} Some of these rocks I learn from Dr. George Dawson, during last summer's explorations, have been proved to belong to the Laurentians and not a separate group.

^{page 165 note 2} Geology of Ireland, chapter i. p. xxi.

^{page 165 note 3} These rocks were suggested by the late Sir R. I. Murchison to be Laurentians; he however subsequently changed his opinion. In the late proposed classification of the West Galway rocks, these have not been included in the so-called Archaean rocks; that distinction being given to the more metamorphosed, but younger rocks in the country to the southward;—rocks that have been proved by their fossils to be of Cambro-Silurian age.

^{page 165 note 4} Geol. of Ireland, chap. xii. p. 194.

^{page 165 note 5} Geol. Ireland, chap. x. p. 177. As a rule the Huronians seem to belong to the “ Schist series,” but some of the Huronian limestones and associated rocks between Port Arthur and the Rat Portage belong to the rock called by Indian geologists “ Sub-Metamorphic rocks.” Some of these limestones are very little altered.

^{page 166 note 1} Selwyn has specially mentioned, that the present boundaries and mapping of this county is only provisional, and that hereafter there will, probably, be found in it tracts of rocks belonging to the Huronians.

^{page 166 note 2} It has been stated,—palæontological evidence proves these different groups;

this however does not appear to be proved. The different flora and fauna were developed and flourished under such conditions as were most favourable; and consequently each different group is most conspicuous, in more or less similar groups of strata; and for this reason such strata are said to be of one age. This often is hard to disprove, ou account of not being able to trace the rocks from one place to another; but when we are able to do so, as is the case with the Carboniferous rocks of Ireland, it is found that the so-called divisions are only lithological. This can also be seen in the Irish Devono-Silurian; take, for instance, the Culfln section, co. Galway, where the lowest rocks contain Llandovery and Wenlock fossils, while over them are strata containing Caradoc fossils, which are succeeded by rocks having typical Wenlock and Ludlow fossils, while in the group above them, according to Davidson, the prominent and nearly only fossil is of a Llandovery type.

^{page 167 note 1} In both these counties these gneissose and granitic rocks are evidently, at least in part, younger than the associated rocks, which have been proved to be, or are probably, of Cambro-Silurian age.