332 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Janlakv, 1906. 



The Scuirr of Eigg. 



At a meeting of the Geological Society held on December 6, 

 Mr. Alfred Harker read a paper on "The Geological Struc- 

 ture of the Sgiirr of Eigg." The mention of this phenomenal 

 mass of pitchstone naturally recalls to mind the very full 

 description which we have had from Sir Archibald Geikie of 

 the island, and the deductions which he has drawn as to the 

 remarkable changes of level which have taken place, and the 

 vast amount of denudation which has resulted in the formation 

 of the Scuir (so spelt by Sir Archibald). The pitchstone is a 

 massive sheet some 400 feet thick, and reposes upon alter- 

 nating basalts and dolerites, which make up the greater part 

 of the island. Beneath the pitchstone there are in two places 

 accumulations made up of fragmentary materials, and these 

 the latter geologist regarded as river-gravels of the age of the 

 pitchstone, which overflowed into the valley of a stream which 

 has since disappeared. The fragments of the gravel have 

 alone been preserved by the pitchstone protecting it from 

 denudation. Mr. Harker is unable to accept Sir Archibald 

 Geikie'sview. He thinks that the pitchstone may have been 

 intrusive, and does not think that its base is reconcileable with 

 that of a river valley. The fragmentary deposit is in one place, 

 he states, a volcanic agglomerate, probably filling a small vent, 

 and the other appears to him as a bedded agglomerate, but 

 this he admits has been re-arranged by water action. There 

 are contained in the deposits abundant blocks of Torridonian 

 and Oolitic sandstone, with fossil wood of Oolitic age, and 

 these are held to have been forced up from below. In this 

 respect there is perhaps some failure of evidence, and some 

 geologists will not regard this explanation as a probable one. 

 It should be added that Sir Archibald adheres to his own 

 explanation of the origin of the fragmentary deposits, and no 

 doubt more will be heard of the matter now that the leading 

 geologists differ radically as to its origin. 



Pleistocene Lake at the Mouth of the 

 Ta-gxis. 



At the same meeting a paper was read by Prof. Edward Hull 

 concerning the " Great Pleistocene Lake of Portugal." The 

 margin of the former lake was probably formed by the granite 

 of Das Vargans and Cunheira. Miocene times are thought to 

 be represented by the Almada Beds, and the Pliocene not 

 being represented, except possibly by certain glacial deposits. 

 Prof. Hull thinks that the period was one of great uplift, and 

 this resulted in the excavation of the sub-oceanic gorge which 

 marks the seaward extension of the River Tagus. Thus the 

 lake was finally drained by the Tagus cutting a channel at the 

 harbour of Lisbon, upon the elevation of the land to about its 

 present level. 



Gla.ciatiorv in Snowdonia. 



Evidence of the Glacial Epoch are numerous in North 

 Wales, as all acquainted with Snowdonia are well aware. Our 



illustrations give two well-marked types of scenery. Fig. i 

 shows a fine series of moraine hillocks near the Devil's 



Kitchen, at the head of N'ant Ffrancon valley ; and fig. 2 gives 

 the rochc-moittonnce appearance of surface-rock resulting from 

 the planing power of a mass of moving ice, taken from the 

 same neighbourhood. 



ORNITHOLOGICAL. 



By \V. P. Pycraft, A.L.S., F.Z.S., M.B.O.U., &c. 

 Humming Birds in EnglaLnd. 



At the meeting of the Zoological Society on November 28, 

 Captain Pam gave a most interesting account of his attempt 

 to start a colony of humming birds at the gardens of the 

 Society, and, though this attempt was frustrated, the greatest 

 credit is due to Captain Pam for the strenuous eft'ort he made 

 to achieve this end. He left Venezuela with about half-a- 

 dozen specimens oiPetasophora iolata, the BoUvian '-violet ears" 

 of Gould's monograph of these birds ; but, unfortunately, 

 onl)' one reached the gardens alive, and this has since died. 

 He fed his birds on a mixture of sugar and meat extract, a 

 diet which seems extremely well suited for these delicate birds, 

 inasmuch as he succeeded in keeping his captives alive, and 

 well, longer than many residents in Venezuela who have 

 continually endeavoured to keep these birds in aviaries, but 

 without success — two months being about the record. 



Humming birds appear to be late feeders, coming out just 

 when other birds are going to roost. They are also heavy 

 sleepers; so much so that Captain Pam found it difficult to 

 awaken his birds after they had finally retired to roost. They 

 appear to be extraordinarily sensitive to shock, so much so 

 that should the cage in which they are confined receive a 

 sudden jar, they lose their foothold — for the feet are remark- 

 ably small, and but little used — and tumble to the bottom of 

 the cage. Whenever this happens, it results in a total loss 

 of the power of movement in the wings ; the birds become 

 unable to regain the perches, and speedily die. 



It was believed that this bird was the first humming bird 

 ever brought into this country alive. But Mr. Pocock points 

 out (Field, December 9) that in July, 1S94, no less than eleven 

 specimens of Truchiliis cuniutus were brought o\-er in the 

 ?.s. Silc, and were ultimately purchased by the late Mr. 

 Erskine Allen, of Gray's Inn. It would be interesting to 

 have further particulars of these birds. 



The Breeding Plumage of Birds. 



In a very short but extremely interesting article in the 

 FicUl, December 2, signed " R. L., ' a new interpretation is 

 given to the "eclipse" plumage of the Mallard and other 

 Anatidas. It is suggested that the " eclipse " dress corresponds 



