358 C. CALLAWAY ON THE NEWEK GNEISSIC 



group, conformably overlying the Dolomite; and he names them 

 " Logan Kock," from Glen Logan or Laggan, where they have been 

 identified by Prof. Bonney as Hebridean. I shall submit evidence 

 to the effect that by faulting, accompanied or followed by powerful 

 lateral thrust, this rock has been thrown over on to the Assynt 

 series to a maximum breadth of about a mile, and along an outcrop 

 of over 15 miles in Sutherland alone. This overlie often produces 

 the appearance of conformity between the Assynt series and the 

 Hebridean. 



b. Caledonian. 



This system is divisible into two well-marked groups. The lower 

 I have recognized only in the Erriboll area ; and from its clear de- 

 velopment in Ben Arnaboll, I have called it the Arnaboll series (b). 

 It consists of grey, granitoid, very felspathic gneiss, overlain by dark, 

 striped hornblende and mica gneisses, passing up through beds 

 of an intermediate character into the ordinary flaggy gneiss which, 

 from its exposure on Loch Hope and in the lofty peak of Ben Hope 

 (3040 feet), I have designated the Hope series (6 2 ). The latter is 

 very uniform in its lithology wherever I have seen it between Loch 

 Erriboll in the north, and Loch Broom, in Cromartyshire, in the 

 south, and from this line eastwards to Lairg, in Sutherland, and 

 Ben Wyvis, in Ross. It is normally a thin-bedded, highly quartzose 

 gneiss, passing into a felspathic variety on the one hand, and into 

 quartz schist on the other. Within the extensive area described, I 

 have not been able to detect any evidence of the reappearance of 

 the Hebridean. Near Lairg, it is true, the Shiness limestone, which 

 is highly crj'stallme, is associated with bands of very massive horn- 

 blende, together with bands and nests of mica, steatite, and several 

 other minerals, all highly crystalline. Prom the general relations 

 of these beds, I am disposed to regard them rather as a local varia- 

 tion of the Caledonian, perhaps due in part to the presence of the 

 limestone, than as an uptlirust of the Hebridean. 



c. Assynt Series. 



1. Probable Age. — Two chief objections are urged by Prof. Heddle 

 against identifying the limestone of Assynt and Erriboll with that 

 of Durness. 



(1) The absence of the Durness fossils in the Assynt group. Sir 

 R. I. Murchison alleges that " an orthoceratite " was found in 

 quartzite on Loch Erriboll, and " orthoceratites" in the limestone near 

 Inchnadamff. The Erriboll fossil was described by Salter, and com- 

 pared by him with Orthoceras (Cameroceras) Brongniartii (Troost ?). 

 It was given to Murchison by Mr. Clark, of Erriboll House, who 

 fixed its locality. The Assynt fossils were discovered by Peach, 

 and handed to Murchison on the spot. Mr. Peach has recently 

 (1882), in a letter to * Nature,' positively reaffirmed the genuineness 

 of the discovery. Unfortunately, none of these specimens can be 

 produced. Many observers, including myself, have since diligently 

 searched for fossils in the limestone, but without success. 



