776 REPORT—1896. 
~* ‘The following Papers were read :— 
On the Geology of the Isle of Man. 
By Professor W. Boyp Dawkins, J/.4., F.R.S. 
The geology of the Isle of Man presents many points worthy of the attention 
ef the Geological Section. The following notes are based on my survey, during 
the last ten years, on the 6-inch scale, and on borings carried out under my advice 
through the thick covering of drift in the north of the island. 
The Ordovician Massif. 
The massif of the island consists of Ordovician clay-slates, phyllites, and 
quartzites, locally much folded and contorted, traversed by numerous volcanic 
dykes, and penetrated at Foxdale, the Dhoon, and Santon by three bosses of 
granite. They are for the most part unfossiliferous, the only three fossils as yet 
found being Palcochorda, Dictyonema, and a trilobite,’ sufficiently perfect to be 
identified with one or other of the Ordovician genera. They are probably the 
south-western prolongation of the Skiddaw slates of the Lake Country beneath 
the Irish Sea. They are of unknown thickness, and have a general dip seawards, 
from an axis running from N.E. to 8.W., the slates and shales forming the 
central nucleus of hills—Snaefel, North and South Barule, Cronk-na-Trelay, &¢.-— 
and the quartzites for the most part occurring in the littoral areas, and more 
particularly along the south-eastern seaboard, from Ramsey to Langness. These 
rocks have been locally very much altered by the heat caused by crushing. Where 
the slates, for example, have been traversed by white quartz veins, the friction, 
caused by the smashing of the quartz into the softer slates, has caused the 
development of mica-schist at the point of contact, and more rarely also of 
hornblende. 
The crush-conglomerates (of Ballanayre and Sulby Glen), mainly occurring in 
the north of the Massif, formed by the smashing of thinly bedded quartzites and 
harder slates, and their being driven into the softer slates, testify to the enormous 
subterranean forces-which have been at work, as Mr. Lamplugh has conclusively 
shown.? The result is a conglomerate, composed of blocks great and small, mostly 
rounded, and some scored like those from the glacial drift, each being covered by 
a thin film of sericite. 
The Carboniferous Limestone of the South. 
The Carboniferous Limestone series is seen in the south of the island, in the 
area of Castletown, Langness, and Ballasalla, to rest on a sea-worn floor of the 
highly contorted Ordovician rocks. At the base is the Red Conglomerate, some 
15 feet thick, out of which the arches at Langness have been cut by the sea. 
It is formed of pebbles, red and white vein-quartz and red quartzite, derived 
from the break-up of the strata below, the grey Ordovician quartzite, with iron 
pyrites, having been oxidised into the red quartzite of the pebble. On this rest 
the thinly bedded limestones and shales of Castletown Bay and Derbyhaven. The 
beds of limestone increase in thickness to the west of Castletown Bay and at Port . 
St. Mary. To the upper portion of this series belong the black and white lime- 
stones and black Poseidonia shales of Pool Vaish, and the interbedded volcanic 
agglomerate, between that place and Scarlet Point. The latter is proved to have 
been the site of the eruption by the Augite Porphyrite of the Stack. 
The dykes of Olivine-dolerite * which riddle the limestone on the shore between 
this point and Castletown and Kentraugh are post-Carboniferous, and are referred 
by Horne and A. Geikie to the Early Tertiary age. The most important of these 
is the Strandhall dyke, which cuts the lode in the Ballacorkish lead-mine, the fore- 
1 Bolton, Geological Magazine, Dec. iii. vol. x. p. 29. 
2 Quarterly Journ. Geol. Soc., vol. li. 1895, p. 565. 
2 Hobson, Quarterly Journ. Geol. Soc., vol. xlvii. p. 432. 
