546 



Alfred Harher — On some Anglesey Dykes. 



Salter enumerates amongst others the following American species 

 in the Durness Limestone ; some of which, however, are too imperfect 

 for accurate identification : — 



Orthis striatiila, Emmons [non Sclilo- 



theim]. 

 Ophileta compacta, Salter. 

 Maclurea matuiina ? Hall. 



Orthoceras arcuoUratum, Hall. 



undnlostr latum, Hall. 



vertebrale ? Hall [very doutt- 



ful]. 



In addition to these, there are among the fossils I received from 

 the Geological Survey of Scotland, specimens of Endoceras in a very- 

 fragmentary condition, but resembling certain small (?) species 

 with very closely approximate septa, described and figured by 

 Billings from the Calciferous group of Canada.^ 



A Cyrtoceras, very probably the Oncoceras ? referred to by Salter, 

 is also in a condition unfit for determination. 



Though the Durness fossils are by no means well preserved, yet 

 it can hardly be disputed that their general facies, as Salter affirmed, 

 is American rather than European. The testimony of the fossils, so 

 far as it goes, is supported by that of the rocks, for we learn from 

 Mr. Peach ^ that in the order of succession of the beds in the North- 

 west Highlands of Scotland an almost exact counterpart is presented 

 of the strata " exposed along the axis of older Paleeozoic rocks, 

 stretching from Canada through the Eastern States of North 

 America." 



" In the latter region," continues Mr. Peach, " the Silurian strata 

 of Sutherlandshire are represented by (1) the Potsdam Sandstone, 

 always described as being vertically piped by ScoUthus, like the 

 " pipe-rock " ; (2) the Calciferous group ; and (3) part of the 

 Trenton Limestone. 



He further argues, that the beds in these widely-separated areas, 

 though probably not contemporaneous, were homotaxial, and he 

 supposes that the species migrated from one province to the other 

 " along some old shore-line or shallow sea," some barrier separating 

 them from Wales and Central Europe. 



IV. "WOODWARDIAN MuSEUM NOTES : ON SOME ANGLESEY DtKES. II. 



By Alfred Harker, M.A., P.G.S., 

 Fellow of St. John's College. 



TN the northern half of Anglesey occur several intrusions of dark 

 hornblendic rocks, some specimens of which were placed by 

 Henslow in the collection made by him for the Woodwardian 

 Museum. These rocks present a type unusual in Britain, and show 

 some peculiarities which are of considerable interest. 



A few years ago Professor Bonney found on the south-west coast 

 of the island some boulders of a rock which he described^ under the 



1 Canadian Naturalist, 1859, vol. iv. p. 361. 



2 Presidential Address before the Royal Physical Society of Edinburgh, Nov. 1885. 



3 Q. J. G. S. vol. xxxvii. p. 137, 1881 : vol. xxxix. p. 254, 1883 : vol. xli. 

 p. 515, 1885. See also Teall, "British Petrography," pp. 81, 82: plates iv, 

 Wvi. 1886. 



