384 KECENT WORK OE THE aEOLOGICAL STJEVEY 



problem was made by Professor Bonney, who described the so-called 

 " intrusive syenite " of Glen Logan, pointing out the occurrence of 

 foliation in the rock and the X.W. strike ; from which he inferred 

 that all the " syenite," with the exception of a few dykes, is simply 

 a rather granitoid variety of the Hebridean gneiss. He showed 

 that its junction with the calcareous series is a faulted one and 

 indicated the direction of the fault. He called attention to a 

 marked fragmental structure in a green schist occurring in the mass, 

 which he attributed to crushing in situ*. 



Similar views to those of Professor Bonney regarding the " Logan 

 Eock " were advanced by Mr. Hudleston, in 1882, who described it 

 as tlie local representative in the Ben-More-Assynt range of the 

 fundamental gneiss, and " as the framework or core round which 

 the newer rocks are folded." He disputed the existence of the 

 " Upper Quartzite," but considered that the section at Craig-a- 

 Knockan shows a regular ascending series from the Silurian rocks 

 to the upper gneiss f. 



The various papers contributed by Dr. Callaway, embracing his 

 researches in the districts of Loch Broom, Assynt, and. Loch EriboU, 

 still further weakened the belief in Murchison's order of succession. 

 Eegarding those areas he maintained that there is no conformable 

 sequence from the quartzites and limestones to the eastern gneiss, 

 that the " Upper Quartzite " is merely a repetition of the lower 

 quartzite, and that the " Upper Limestone " is either a repetition of 

 the dolomite of the " Assynt Series " t ot an integral part of the 

 Archaean series, as at Loch Ailsh. Recognizing the lithological dis- 

 tinction between the western and eastern gneisses, he grouped them 

 in two great formations of Pre-Cambrian age — (a) the Hebridean, 

 (h) the Caledonian, the latter resting unconformably on the former. 

 Though the eastern gneiss (Caledonian) overlies the Silurian strata 

 at certain localities, he contended that it had been brought into this 

 position by overfolding and faulting without materially altering 

 its original structures. In the district round Loch Broom, and in 

 Assynt, the " Logan Eock " (Heddle) is regarded as part of the 

 Hebridean gneiss brought up by faults, showing signs of crushing at 

 the points of junction with other strata ; at Loch EriboU it is re- 

 garded as the base of the Caledonian gneiss. At Loch Broom the 

 Hebridean gneiss, bj^ means of faulting, is brought into contact 

 with almost every member of the Silurian series in turn, and slightly 

 overlies them ; while in Assynt, where it is sometimes accompanied 

 by the Torridon Sandstone, this gneiss is thrown over on to the 

 Silurian series, " the overthrow increasing in breadth northwards, 

 so that in Glencoul it is more than a mile wide." 



In the appendix to Dr. Callaway's paper (Quart. Journ. Geol. Soc. 

 vol. xxxix. p. 416) Professor Bonney describes the microscopic 



* " Petrol ogical IN'otes on the Vicinitj- of the Upper Part of Loch Maree," 

 Quart. Journ. Geol. Soc. vol. xxxvi. p. 93. 



t " First Impressions of AssjTit," Geol. Mag. dec. 2, vol. ix. p, 390. 



I Dv. CallaAvaj applied the term " Assynt Series "' to the Quartzites, Fucoid 

 beds, Salterella-grit, and Limestone of Murchison's Silurian succession. 



