•2O0 



SCIENCE-GOSSIP. 



and about which opinions are divided, some 

 assigning them to the Devonian series, and others 

 to the Permian. These beds will be again referred 

 to when this locality is dealt with. 



Having discussed the sedimentary rocks, I will 

 now briefly mention the igneous rocks. Volcanic, 

 Plutonic and Intrusive are all represented. The 

 former has a grand example in the Scarlet Stack 

 and Scarlet Point, a huge sheet of basalt. The 

 plutonic rocks have their principal representatives 

 in the granite "bosses" at Foxdale and Dhoon 

 Glen, and in connection with which there are 

 many examples of aplite, pegmatite, greisen, etc. ; 

 one or two exposures of diorite being found on the 

 Langness peninsula. Intrusive rocks are abundant 

 in all the older rocks of the Island, and are, gener- 

 ally speaking, trap, felsite, and quartz porphyry. 



For the purpose of relating the more minute 

 geological features, I think it better to describe 

 them under the heading of excursions to the 

 different localities, instead of grouping them 

 together in their series or otherwise, and this I 

 will now do, commencing with the little glen and 

 bay at Groudale, a short distance to the north of 

 Douglas. 



Excursion to Groudale. 



The cliffs at Groudale. are the usual Silurian 

 rocks already referred to, and resting thereon is a 

 great thickness of glacial drift. At one point it is 

 from fifteen to twenty feet in depth, and there is no 

 doubt it was very much more. It is exposed to 

 this depth near the " Sea-lions Cave," where it has 

 been excavated for the purpose of laying a miniature 

 railway. A very noticeable feature of this drift 

 section in particular is the variation of the matter 

 composing it, being really made up of different 

 beds. On the top is a light-coloured clay, full of 

 pebbles of granite, trap, slate, etc. Then comes a 

 bed of dark-coloured stiff clay, without any pebbly 

 constituent. There again is another bed similar to 

 the first mentioned, but of a coarser character, 

 and containing some fairly large boulders. This 

 difference does not extend any great distance, 

 the middle bed gradually thinning out, and the 

 other two coming together. The headland on the 

 top of which I observed this secjion is called Clay 

 Head, I suppose in allusion to its immense covering 

 of this material. 



In the Groudale Glen there is an instructive 

 example, though not a very large one, of a cation. 

 A small stream coming down the mountain to join 

 the larger stream in the glen has cut its way deep 

 through the slaty rock. Here we have a good 

 instance of water-wearing action alone, atmo- 

 spheric agency not having done much, as the sides 

 of the caiion are practically vertical, at some 

 points being twenty to thirty feet in height. In 

 this place there are several small cascades and 



waterfalls, showing the difference in the hardness 

 and texture of the rocks, some wearing away a great 

 deal faster than others. 



At the Groudale Bay there is a small example of 

 what is probably at times a " storm beach." The 

 shingle is thrown back from the shore and forms a 

 bank across the mouth of the stream which flows 

 through the glen. The water gradually finds its 

 way through this block of shingle, but its transport- 

 ing power is very much reduced, the shingle bar 

 acting as a filter, and the stream has to deposit all 

 large matter inside the bar, thus lengthening the 

 bar up-stream and tending to the formation of a 

 lake. As, however, the bay and stream are so tiny, 

 there is not much chance of any great geological 

 change ; but the example is an instructive one to 

 the student. 



Excursion to Laxey. 



Probably the first thing one notices, when stroll- 

 ing along the shore of Laxey Bay, is the greenish 

 colour and comparatively coarse nature of the 

 sand. On examining a small quantity of this under 

 the microscope, it is found to consist of particles 

 of quartz, both the opaque white variety and rock- 

 crystal, slate, copper ore, lead ore, etc. The 

 greenish colour is imparted by the grains of slate, 

 lead and copper ore. Here one can well observe 

 how the material of the locality is being prepared 

 and laid down to form what will in future geolo- 

 gical ages probably be a sandstone or gritstone. 

 The particles of slate are derived from the break-up 

 of the adjoining cliffs, the copper, lead and quartz 

 being produced from the numerous veins which 

 intersect these rocks in all directions. The stream 

 which flows through the Laxey glen no doubt acts 

 as a great transporter of material from the high 

 ground which terminates in the Snaefell mountain. 

 The operations of the Great Laxey Mining Com- 

 pany, and the Snaefell Lead Mining Company, 

 where the deplorable disaster took place some 

 time ago, doubtless add to the deposit. The coarse 

 nature of the sand is probably due to the fact that 

 the bay is a rather secluded one, the wearing 

 action of the waves being thereby reduced. 



The prevailing rock at Laxey Bay is, again, the 

 Silurian slate or flag ; the beds dipping towards 

 the sea at a fairly high angle. The colour is dark- 

 grey ; it is hard, and regular in bedding. On 

 breaking some of these, I once found what might 

 have been a fossil of some kind, but of what I 

 could not then make out. Since then I have heard 

 that certain marks in these rocks were examined 

 by Mr. J. Taylor, in 1S62, and Mr. T. Grindley, in 

 1865 ; and had the impressions been discovered in 

 later strata, they would no doubt have been taken 

 for footprints. What I found was a small oval 

 patch of a lighter colour, harder than the surround- 

 ing slate and about a couple of inches long. 



