270 



HARD WICKE'S SCIENCE- G OSS I P. 



clay containing quantities of angular rock- fragments : 

 this deposit thins away up each bank of the valley, 

 but is of considerable thickness in the middle. The 

 origin of this valley "till" is perhaps difficult to 

 decide, but as it contains fragments of rocks foreign 

 to the locality, and as the fragments generally are in 

 a most confused state, we think it possible that it, like 

 many others in the island, has been caused by small 

 local glaciers which, without being of sufficient dimen- 

 sions to striate and groove the rocks over which they 

 passed, were, nevertheless, able to tear and fracture 

 the tilted strata and veins and mingle them with the 

 coarse clay which they gathered in their course, from 

 decomposed surfaces. These valley clays are often 

 covered by another drift deposit which can be traced 

 on almost all parts of the island, but which is not 

 allied to the former ; these again being sometimes 

 covered by blown sand, renders the true position of 

 these beds difficult to determine, except in such char- 

 acteristic examples as the one above referred to. 



Leaving this fine bay, the rocks again rise and we 

 suddenly enter upon a remarkable conglomerate, the 

 contact of which with the rhyolitic rocks, is very 

 defined. This conglomerate is of a rich bluish-brown 

 colour and consists of rounded and subangular frag- 

 ments of felsites, syenites, hornstones, and a some- 

 what dubious sandstone ; near the base of this bed the 

 boulders are of great size, often from six to twelve 

 feet in diameter ; this part of the formation is well 

 seen between Fliquet Bay and La Tour, and the con- 

 glomerate itself extends round to Bouley Bay, thus 

 occupying the whole of this extreme corner of the 

 island. 



At Bouley Bay, where it joins the rhyolites again 

 the latter rocks present a most remarkable and diver- 

 sified appearance ; their general structure merging 

 from a flow, having all the appearance of stratifica- 

 tion, to that of a highly spherulitic character. It is 

 this latter structure that has presented such difficulties 

 in determining this rock. In one part, the spherules 

 are of a reddish colour, and of the size of peas im- 

 bedded in a greenish matrix ; in others, they occur as 

 much as two or three inches in diameter, but not so 

 well defined as in the finer examples ; but the most 

 normal form is that in which the natural flow of the 

 lava is preserved. This latter foi^m merges into the 

 spherulitic one and shows how the formation of the 

 concentric nodules occurred ; for in a small hand 

 specimen can be observed the lines of flow, often 

 containing quartz, breaking up into long oval bodies, 

 these again gradually becoming spherular. If a frac- 

 ture be made so as to show the structure of these 

 nodules, it will be seen that they are almost oolitic 

 in their appearance, and are moreover rarely blended 

 together ; in most instances a crescent-shaped frag- 

 nient of quartz forms a half-ring round the nucleus, 

 but it is remarkable that this crescent occupies various 

 positions in even adjohiing spherules. It is also highly 

 probable that this quartz contains fluid cavities, but 



this we liave not yet had an opportunity of ascer- 

 taininc:. 



The higher ground of this locality consists of a 

 very decomposed form of this rock, the real structure 

 of which is thereby much obliterated. These rhyolites 

 now merge gradually at Vicart Point into the syenite 

 again, which latter is overlaid by a small bed of con- 

 glomerate of a much older appearance than that 

 already referred to, being of a much finer composition 

 and having been apparently subjected to fusion. At 

 Les Rouaux the syenite is overlaid by clayslate, and 

 a fault in the junction of the beds has formed a chasm 

 on the shore varying from eight to twelve feet in its- 

 present depth, and extending for a considerable dis- 

 ance ; one ledge of this cleft being clayslate and the 

 other syenite. The syenite rocks now predominate, 

 but near Sorel enormous boulders of basalt and 

 diorite, many of which contain thirty or forty cubic 

 yards, occur not only on the shore, but also on the 

 high ground. These appear to owe their origin to- 

 the same causes as the clays already referred to, and 

 most decidedly suggest the former existence of glaciers, 

 particularly as there is a fine example of a morainic 

 deposit at this point, 



A short distance inland, in the parish of St. 

 John, are the celebrated quarries of Mount Mado, 

 from which are obtained two fine varieties of 

 syenite, highly adaptable for building purposes, 

 the one is a finely grained pinkish variety, whilst 

 the other is a coarser and whiter kind. About a 

 mile from here a "china-stone" is largely workedj 

 for export, this aplite or bi-granite is an interesting 

 rock, it is intersected by a large vein of massive 

 quartz, containing traces of molybdenite. Returning 

 to the coast at Sorel we have a large funnel-shaped 

 cavity, known as the Crciix die 77>, this is a fine ex- 

 ample of the results of the action of the sea upon the 

 base of a softer vein of rock ; the sea having access to 

 the lower portion causes the superincumbent mass to 

 gradually detach and fill up the cavity thus caused, 

 this in turn becomes removed in the same manner, 

 until the whole of the softer mass disappears, forming, 

 as in this instance, a creux, but in others, as seen near 

 Bouley Bay, a tall narrowing gully with vertical sides 

 often a hundred feet in height. 



At Greve-de-lecq the syenite contains fine cone- 

 in-cone crystals of quartz, similar to, but not so fine 

 as those which we mentioned as occurring at La 

 Rocque ; some of these are well shown in section on. 

 the water-polished boulders and are very beautiful 

 —a deposit of felspar occupying an inch of space 

 between the cones. 



All about this part of the coast-line are numerous 

 caves, some of which are of considerable dimensions ; 

 these caverns are principally washed by the sea, except 

 at low tides, but there are some far up out of reach 

 of the waves, but bearing evidence of having been 

 once accessible to the ocean. These caves may have 

 been formed in this manner. The syenite in which 



