THE object of this communication is to describe the gradual change from dolerite to hornblende-schist as it may be observed in two more or less parallel dykes which occur in the Arch~ean gneiss of the northwest of Scotland, near the village of Scourie in Sutherlandshire. The northern promontory of Scourie Bay is named on the Ordnance map Creag a'Mhail. Near this point two dykes of basic igneous rock may be seen. The one to the south is about 30 yards wide ; it has been more affected by denudation than the surrounding gneiss, and its course is thus marked b~' a depression which is occupied by the sea at high tide. • short distance to the north of the actual promontory is another dyke, about 20 or 30 feet wide, of similar character, which terminates westward in a vertical cliff. This may be traced in a south-easterly direction down to a small beach where the southern dyke is again seen, and from this point the two dykes may be followed, running parallel to each other towards the southeast , for a distance of a quarter of a mile or more. The prevalent strike of the gneissie banding in this district is E.N.E. and W.S.W., with a moderate dip to N.N.W. The dykes therefore cut across the strike and cannot possibly be regarded as bands in the gneiss. On the opposite shores of Scourie Lake (Loeh a' :Bhaid Daraich) and close by the side of the road to Laxford Bridge (three quarters of a mile from the Scourie Hotel), the dykes again make their appearance. Prof. ]~lake first recognized the northern dyke at this spot on the occasion of our joint excursion to the northwest of Scotland in the summer of 1883. This dyke is here the wider of the two and forms a portion of the conspicuous hill which overlooks the lake. The southern dyke produces a marked gap to the south of the hill. The distance between the two dykes is only a few yards. The junction-planes of gneiss and dyke are nearly vertical, and the fact that they cut across the gneissic banding is most clearly shown. From this point the dykes may be traced to the southeast for more than a mile. What becomes of them ultimately in this direction I do not know ; but, so far as I followed them, they keep very closely to the same straight line and preserve their lithotogical characters (subject to such exceptional variations as will presently be described) with as much persistence as the dykes in the Carboniferous region of the north of England. The rock forming these dykes occurs in two strongly marked varieties. The one is a moderately coarse-grained, crystalline,

The term Whin Sill is applied in the north of England to the intrusive sheet of basic igneous rock which forms such a marked feature in certain portions of the Lower Carboniferous district of Durham, Cumberland, and Northumberland. It is unnecessary, on the present occasion, to describe the stratigraphical relations of the rock, because full details are to be found in the papers cited above, and especially in those by Prof. Sedgwick and Messrs. Topley and Lebour. For some time there was a discussion as to whether the rock was intrusive or interbedded, but this discussion may be regarded as having been closed by the publication of the able paper by Messrs. Topley and Lebour. It is now admitted on all hands to be intrusive. To give some idea of its extent, I may mention that it is exposed as an inlier in Teesdale for a distance of many miles. It reappears in the Cross-Fell escarpment in Cumberland, and may be traced thence, with slight interruptions, across the county of Northumberland, to the sea-coast at Dunstanburgh, following in a general way the strike of the beds with which it is associated. As the strike bends round to the N.W. in the northern portion of Northumberland, the Whin Sill reappears on the coast at Bamburgh, and may be traced from this point to Kyloe, where it is last seen. The distance from the point in the Cross-Fell escarpment, where it first appears, to Dunstanburgh is about 60 or 70 miles. Speaking

Tm~ object of the present paper is to give a petrological account of some North-of-England dykes. The specimens on which the observations are based were mostly collected by myseff during the winter of 1881-82 ; a few, however, were given me by Prof. Lebour and other friends,In the microscopic work I have derived great assistance from my friends Mr. rAnson of Darlington and Dr. Trechmann of Hartlepool. To Mr. rAnson I am indebted in another way ; for he kindly handed over to me the analysis of the Great hyton rock which was prepared for him by Mr. Steck. My indebtedness to the latter gentleman, and also to Mr. Stead of ]~iddlesborough, will appear in the sequel. Without the valuable chemical work communicated by these gentlemen my paper would indeed be incomplete. It is no part of my purpose to describe the mode of occurrence of these dykes, and therefore the general course of each is indicated mainly by reference to works already published. One or two new facts of importance are, however, given ; especially in relation to the dying-out of dykes beneath the surface.The dykes are first of all described in the order of their occurrence from south to north, and at the conclusion of the paper some general remarks on their mutual relations are given. T~ CL~w~r.A~rD, Cocx~rm, A~r]) AR~A~a-WAITE DrK~.Literature.

In 1892 I described, in conjunction with my colleague Mr. Horne, a peculiar rock, essentially composed of orthoclase and melanite, under the name of borolanite. The type-specimens came from the plutonic mass which lies to the north of Loch Borolan, in Sutherlandshire (1 in. sheet 101). During the preparation of the paper on borolanite our colleague Mr. Gunn discovered two dykes of a closely related rock traversing the Torridon Sandstone in the Coigach district of West Ross-shire. The rock of these dykes was described in an appendix to our paper. It contains nepheline and ægirine, in addition to orthoclase and melanite, and is therefore allied, both as regards mode of occurrence and mineralogical composition, to the Tinguaite group of Rosenbusch; but as melanite is an important constituent it was classed with the borolanites.

In his diary the rock is called a granite, but in a footnote he adds that it was a coarse-grained basalt. Vol.5.~.i' ' RoCKs .~Xl, l,oSslLs l.'l'~..~l ~'l~.~Xz aosm' l,~xl,. 451 determined by him to be of Upper Jurassic age. The facf, of these !bssils having been %und on the basalt also influenced Dr. Nansen in referritig this rock, in part at least, to the Jurassic period. Evidences of recent, changes in the relative level of land and se~ are referred to in Dr. Nansen's book. Thus, Mr. Jackson's hut is '