220 



SCIENCE-GOSSIP. 



with dykes of felsite and quartz porphyry, and 

 veins of quartz and copper ore. The copper is 

 found in sufficiently large quantities for the ore to 

 be worked for commercial purposes. 



Here again the combination of schist and 

 conglomerate makes the scenery grand, rugged, 

 and fantastic. The cliffs are not very high, and 

 gradually run down to the water, but at their 

 highest point they are covered by caps of 

 conglomerate. These are carved into all manner 

 of strange and weird figures, and altogether the 

 sight is very startling. The respective colours at 

 this point are different to the arch previously 

 mentioned, the schist being a brilliant claret 

 colour, and the conglomerate of a greenish hue. 

 On breaking some of the pebbles of these " caps," 

 I found quartz, quartzite, slate, trap, felsite, schist, 

 etc., the felsitic ones having a strong resemblance 

 to the dykes of the vicinity. This shows that some 

 of the material, at any rate, for the manufacture of 

 this "pudding-stone" has been taken from the 

 rocks of the locality. These caps were composed, 

 besides pebbles, of angular pieces of slate, schist, 

 etc., the rock partaking both of the character of 

 a conglomerate and a breccia. This very probably 

 denotes the top of these beds, as a certain amount 

 of the angular material had not time to become 

 rounded, and formed into pebbles before the deposit 

 was rendered inaccessible to the action of the 

 waves. This occurred, no doubt, owing to a 

 depression of the land just previous to the time 

 when the Carboniferous beds were laid down. 



I was not able anywhere to find a felsite dyke 

 intruding on the conglomerate beds, and think it 

 very probable that those dykes were formed prior 

 to the deposition of these beds. Assuming that 

 the pebbles previously mentioned were portions of 

 the dykes in question, then their origin must have 

 been subsequent to the time of the Lower Silurian 

 slates into which they intrude, and prior to the 

 formation of the Carboniferous system. 



I made a microscopic examination of a thin 

 slice of felsite from one of these dykes, and 

 found the rock consists principally of quartz and 

 felsitic matter. It is of a greyish hue and very 

 sombre in appearance. The quartz occurs as 

 small grains or patches, but never idiomorphic. 

 What little felspar can be recognized by the aid 

 of the polarizer is very much decomposed and 

 turbid. The felsitic ground mass is of the usual 

 " fleecy " character, and of a grey-brown colour. 

 The quartz is generally clear and glassy ; it 

 contains inclusions, and is somewhat fissured. The 

 slide bears a great resemblance to the quartz 

 porphyry I have already described from Laxey, 

 except that there is no signs of schistosity in this 

 one. It is somewhat similar to a felsite I obtained 

 in the neighbourhood of Snowdon, that one only 

 differing from the Langness specimen by contain- 



ing small cubes of pyrites and having the felsitic 

 base of a strong green colour. 



Having now reached the limit of Castletown 

 Bay in this direction, we will return and take the 

 opposite course. 



From Castletown to Port Erin. 



The walk along the coast from Castletown to 

 Port Erin is an exceedingly fine one from a geo- 

 logical point of view. Immediately on leaving the 

 town the Carboniferous limestone is seen exposed 

 on the shore in beds of about two feet in thickness, 

 of a very dark colour, dense texture, and very fossili- 

 ferous. Some little distance further is a quarry 

 where the stone is obtained and dressed for build- 

 ing purposes. The rock breaks with the conchoidal 

 fracture peculiar to the mountain limestone and 

 gives forth a metallic sound when struck with the 

 hammer. It appears to form a fairly good building 

 stone, but I should imagine it would not last long 

 in such an exposed neighbourhood. Near by are 

 some lime-kilns hollowed out of the cliffs, showing 

 that at some time the stone has been burned for 

 lime, but the kilns appear to be now disused. 

 On following the coast-line for a short distance, 

 further the limestone disappears, and in its place 

 there is found an immense sheet of basalt accom- 

 panied by beds of volcanic agglomerate, ash and 

 dust. Some little distance out to sea, and only 

 accessible at low tide, there stands the huge 

 basaltic pile known as the Scarlet Stack. These 

 rocks form a narrow strip all along the coast from 

 the south-west of Castletown, by the Scarlet Stack,, 

 and terminate near the Poolvash Bay. They are 

 splendidly exposed as a rugged, low cliff, or fore- 

 shore, while their direction seaward is marked by 

 the low-water reef known as " Lheeah Rio '" in. 

 Castletown Bay. This huge contemporaneous 

 sheet is divided into various deposits differing both 

 in regard to structural characteristics and the 

 time of formation. Beds of coarse agglomerate, 

 containing baked fragments of rock, are seen. 

 Ledges of fine tuft are also visible. Ridges of 

 exceedingly vesicular lava appear, and a broad 

 dyke of basalt or dolerite breaks through the tuffs 

 and agglomerates, and eventually finishes in the 

 Scarlet Stack. Here, without any doubt, we see 

 the signs, and what is left, of an ancient volcano 

 The ash and agglomerate beds in some instances 

 contain fossiliferous remains of various kinds, 

 showing that some portion of the eruption, at any 

 rate, was submarine. The broad ridges of vesicular 

 lava, however, point to eruptions at a later date, 

 and when a land surface existed. The basalt is of 

 one or two different kinds, and I shall describe 

 them later when referring to their microscopic 

 examination. 



The colour of this sheet varies in different places 

 according to the particular deposit. The normal 



