SCIENCE-GOSSIP. 



201 



"Whether this is one of the marks above referred to. 

 as examined by those gentlemen. I am unable to say. 

 A walk along Laxey Bay reveals several interest- 

 ing features. At one point there are some immense 

 boulders of a rock containing ironstone. These 

 have evidently at some period been brought down 

 from the high ground above, as they are not 

 :... They are of slate, quartz, trap and pyrites, 

 and in some parts there are "pockets" of oxide 

 of iron of an ochreous nature. 



At the Douglas end of the bay there are some 

 large blocks of a peculiar convoluted nature. 

 These rocks appear to form an intrusive mass of 

 igneous character, and no doubt belong to the 

 same family as the other "intrusions" in the 

 island, viz . felsite or trap. 



I brought a piece of a dyke from this spot, 

 though not from the dyke just referred to, and a 

 microscopic examination leads to the inference 

 that it is a quartz porphyry. At any rate, it is a 

 micro-quartz porphyry. The rock is composed of 

 a felsitic base and quartz. The long axes of the 

 quartz grains all point approximately in one 

 direction, and the rock has a banded or schistose 

 appearance. In the section one or two com- 

 paratively large crystals of quartz are present, 

 and one quartz grain contains a negative crystal 

 with a minute bubble. Very little felspar is present, 

 and this is so decomposed that it would be im- 

 possible to distinguish it without the aid of the 

 polarizer A little magnetite is also present in flakes. 

 The quartz is all separated by layers of the fleecy 

 base, and the rock somewhat resembles fig. 72B., 

 p. 290, in •' Harker's Petrology." In one instance 

 a large piece of quartz is found as an " eye," the 

 other quartz and felsitic matter being arranged 

 round it in a "flow " structure. The quartz does 

 not contain many inclusions of a comparatively 

 large size, but I noticed in one grain a "knee- 

 shaped" crystal of rutile, and in many cases 

 minute specks of dusty matter can be observed. 

 I think there is little doubt that this rock was 

 . inally a " felsite," which has been altered by 

 - amic metamorphism, and had the schistose 

 dure induced. The intense pressure to which 

 it has been subjected has practically obliterated 

 the character; ill the minerals, except the 



quartz, which by reason of its hardness has better 

 .1 the pressure, converting the felspar 

 probably into a mka, and, by the production of a 

 ase which separates the quartz, brought 

 about the lamination Thii characteristic can be 

 baerved in .1 ha . bnl much better 



n un'ler the microscope. 

 In the village of Laxey a large quantil 



lining 

 rnpany Ai th- 



:t of ,late, trap, quart 



only are worked for commercial purposes. By the 

 kind permission of the Company, I was permitted 

 to make an inspection of the surface works, where 

 the extraction of the ores is carried on. The 

 whole process, from beginning to end, is a most 

 interesting sight, even the finest mud resolving 

 itself into the separation of the different ores by 

 means of their specific gravities. 



From the lead ore, a quantity of silver is 

 obtained, sometimes amounting to more than 100 

 ounces of silver to the ton of ore. A great amount 

 of crystalline, opaque, milky quartz is also obtained 

 from the mines, where it is found lining veins of 

 the metal. 



Excursion to Port Soderick. 



The formation here is the usual Silurian rock 

 which is overlain by Glacial clay. The somewhat 

 monotonous rocks are varied by several caves, 

 which are, however, of no great dimensions. A 

 brief examination of them suffices to show that 

 they have been made by the mechanical action of 

 the waves. Chemical agency has had nothing to 

 do with their formation, as it has in the case of 

 the large caves of Derbyshire. One portion of the 

 Smugglers' Cave is evidently the result of the 

 shifting of the rocks along a joint or fault. 



At this spot there is a good beach of shingle and 

 pebbles, and a search along such beaches generally 

 results in the discovery of a few, at any rate, 

 interesting pebbles. Here I found a large boulder 

 of exceedingly tough dense rock of a light blue-grey 

 colour, and so exceedingly hard and compact that 

 it was difficult to knock off with the hammer a few 

 specimens. It was crossed here and there by fine 

 veins of quartz, and appeared from its macroscopic 

 characteristics to be either a very close-grained 

 felsite. similar to one I once obtained in the 

 neighbourhood of Penmaenmawr, North Wales, or 

 a quartzite. On examining a thin section under 

 the microscope, the quartzite theory proved to be 

 correct. The slide shows the rock to be made 

 of quartz grains, closely compacted together. The 

 interstices are filled with a "paste" of minute 

 quartzose matter which in places forms compara- 

 tively large patches. The quartz crystals or grains 

 are traversed by rows of fluid pores and minute 

 inclusions, and fissured in places. The fissures 

 generally are in one direction, and as a rule at 

 right angles to the lines of inclusions. There is 

 practically no felspar, but little turbid patches are 

 seen which may be this mineral decomposed or 

 altered by crushing ; small flakes of magnetite an to 

 be observed, and here and there portions of the rock 

 are found which are unaffected by (he polarizer 

 .and seem aim ■ ■■ I liese patches are, I 



believe, quartz "dust, tnd probabl n preai nl 

 ite result of mi I ndary 



'. la not seen at all, and from ih" •■ < ceding 



