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YORKSHIRE PETROLOGY. PART II. THE LAMPROPHYRES. 
BY THOMAS TATE, F.G.S. 
A series of eruptive rocks, somewhat alike in composition and age, 
extends along tlie border of West Yorkshire from Ingleton by way of 
Dentdale, Garsdale, Sedbergh, around the flanks of Howgill Fells, 
and thence to Middleton-in-Teesdale. The members of this series 
exposed in the neighbourhood of Ingleton have already been 
described in a former paper (vol. ix., page 380). In the present 
communication it is proposed to deal with the allied rocks, as they 
may be studied in the Dentdale area some ten miles further north. 
Leaving Ingleton by the old river course and skirting Whernside 
we may descend by Deepdale into the lovely valley watered by the 
River Dee. Below Dent we find seven or eight exposures of these 
traps in two localities ; three in a stream to the west of Millbeck on 
the south side of the dale, and five in Helmsgill running up the 
northern slope. A walk of about a mile down the valley from Dent 
brings us to Helmswood, and ascending the beck till past the water- 
fall we enter upon the open pastures 1} ing at the foot of Helmsknott, 
and it is here, within a distance of one hundred and thirty yards 
from the fall, that we meet with a series of five dykes exposed in or 
near to the bed of the stream in regular sequence as we ascend. The 
chronology of the beds in contact with the intrusions in the Ingleton 
area is somewhat obscured by the faulted character of that district, 
but the series of mica-traps outcropping in Helmsgill presents no 
such difficulty, the succession being quite clear. The beds intrusively 
penetrated belong to the Coniston Limestone and its underlying 
calcareous shales (Ordovician), all dipping uniformly at a moderate 
angle to the south-west. The uppermost (geologically) of these 
intrusions occurs near the waterfall, on the west bank of the stream. 
It weathers to a warm brown tint, is somewhat angular in outline, and 
partially moss-hidden, not more than three or four square feet being 
exposed. Of all the series this is the toughest and best preserved 
rock. A fresh hand-specimen is purple-hued, due to an intimate 
