230 



PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Nov. 16, 



which afforded the Orthoceratite presented to me by Mr. Clark and 

 now laid before the Society. 



Mr. Salter says that this large Cephalopod resembles the Orthoceras 

 ( Oameroceras) Brongniartii * ; and he thus describes the specimen : 

 " This fragment (from the upper quartz-rock of Eriboll, collected 

 by Mr. Clark), imperfect as it is, shows enough to distinguish it 

 specifically from the large-tubed Orthoceras duplex of the Scandina- 

 vian rocks, inasmuch as the ridges on the great lateral siphuncle 

 (lines of junction with the septa) are closer and less oblique. The 

 septa themselves are very convex. 



" The comparison with American species cannot well be made, for 

 want of more complete drawings of the latter. But the Irish fossil 

 identified by Portlock with an American species (0. Brongniartii, 

 Troost ?) seems to be the same as our fossil. In neither is the 

 siphuncle strictly lateral ; and hence this species tends to connect 

 Oameroceras with the more ordinary forms of the genus." 



The occurrence of this fossil in the quartz-rock leads to the belief 

 that, Avhen the limestones of Loch Eriboll are searched with the 

 same assiduity as was applied by Mr. Peach to their equivalents in 

 Durness, other fossils will also be detected in them. 



The upper limestone, which is thin, and not persistent for any con- 

 siderable distance on the strike, is seen to graduate upwards under 

 Meol-bad-vartie into quartzose, felspathic, micaceous, thin-bedded 

 strata, which in parts assume a greenish tinge, and so pass upwards 

 into that series of micaceous, felspathic, and quartzose flagstones 

 which in parts have gneissic characters. 



All these overlying strata repose conformably at slight angles of 

 inclination on the whole of the quartzites with limestone, and with- 

 out any break or separation. 



N.W. 



S.E. 



Fig. 8. — Section at Tordleadh. 



1. Quartz-rock. 



2. G-neissose flag- 



stone. 



3. Quartz-rock. . 



4. Gneissose flagstone. 



Dip. 35° S.E. 



Prof.Harkness has transmitted to me a section (fig. 9) of the alterna- 

 tion of the quartz-rock and upper gneiss at a spot called Tord-leadh, or 

 the Green Knoll, to the N.E. of the House of Eriboll, which completely 

 sustains this view of the gradual and conformable transition, and shows 

 that there are considerable spaces where no intercalated igneous 

 rock is visible. It is true that Prof. Harkness has observed what 

 Prof. Ramsay and myself failed to detect (as well we might m a 

 lofty mountain-escarpment),— viz. the existence of 3 feet of inter- 

 stratified igneous felstone, represented in fig. 9. It is, however, to be 

 observed, that not only does this felstone not interfere with the regular 

 sequence and conformable overlying succession, but, instead of lying 



Portlock, Geol. Eep. pi. 28. f. 4. 



