1871.] GEIKIE TEETIARY VOLCANIC EOCKS. 289 



dip of the rocks of the island is from north to south, the Oolitic 

 series is best seen at the north end, whence its different groups of 

 strata slope northward, until they finally disappear under the vol- 

 canic series at the Bay of Laig. The following section shows the 

 order of succession among these rocks :- — 



Dolerites, basalts, &c. of the plateau. 



(4) Clay, with ammonites, belemnites, &c., seen for a short space on the 



beach of the south side of Laig Bay. 

 (3) Estuarine shells and limestone with Ct/clas, Ci/prides, Ostrea, &c. 

 (2) Thick white and yellow sandstones, in some places abounding with 



fragmentary plants, and at other parts strongly calcareous, with 



numerous casts of Cyclas, &c. 

 (1) Estuarine shales and limestones, with fossils similar to those in No. 



3, and with reptilian bones. 

 Base of series not seen. 



From the general character of these beds, I am inclined to regard 

 them as on the same horizon with the estuary beds of Loch StafEn, 

 and with those which in Raasay come in between the Lias and the 

 Tertiary volcanic rocks — that is, as belonging to the Lower Oolites. 

 But this subject will require further consideration when the fossils 

 have been determined. 



D. YoLCANic Series. 



The Oolitic strata of Eigg are overlain by a cake of igneous rocks, 

 which, though it caps the northern cliiFs, dips southward with the 

 underlying strata, until it reaches the sea at Laig Bay on the west 

 side, and at Kildonan on the east. I^Torth of a line drawn between 

 these two places the igneous capping has been reduced by denuda- 

 tion to a mere narrow strip, forming the tableland of Beinn Bhuidh ; 

 south of the same line, it covers the whole breadth of the island. 

 Yet, although the general inclination of the igneous and aqueous 

 rocks is in the same direction, a careful survey of them shows that 

 the former lie unconformably upon the latter. At the south side 

 of the Bay of Laig, the basalt-rocks rest upon the clays of group No. 1. 

 As the former are inclined at a slightly less angle than the latter, 

 they soon creep over their edges, so as to lie upon the shales and 

 and limestones No. 2. These continue as far as Dunan Thalasgair ; 

 but there the basalts, after slowly creeping over their denuded 

 edges for nearly two miles, overlap them, so as to come upon the 

 massive sandstones of group No. 2. The apparent conformity, there- 

 fore, of the volcanic rocks with the Oolitic strata of the inner He- 

 brides, which has led to the belief that the volcanic phenomena 

 were of Oolitic age, is in reality deceptive. I shall on other occasions 

 have to point out the varied horizons on which these volcanic 

 masses rest. 



The igneous rocks of Eigg may be most conveniently described 

 under three heads : — 



1. The Basalt-plateau, marking the oldest eruptions, 



2. Intrusive bosses, sheets, dykes, and veins. 



3. The pitchstone coalees of the Sour, a relic of the last eruptions. 



