274 MR. H. H. AEIfOLB-BEMROSE ON [Aug. I907,. 



bands hold good for the two upper bands of similar structure, we 

 should have the following section, which is correct for the lowest. 

 31 feet and probably not far out for the upper 25 feet : — 



Thickness 

 in feet. 



A. Fine-grained olivine-dolerite 14 



B. Coarse-grained olivine - dolerite, in which the felspars 



predominate 11 



C. Ophitic olivine-dolerite, in which the augite predominates . 6 



D. Coarse-grained olivine-dolerite similar to B < 11 



E. Fine-grained olivine-dolerite similar to A 14 



Total 56 



The intrusive rock, which has penetrated into the lower lava of 

 the northern area, is found at different horizons in the lava, resting 

 upon the limestone below the lava and upon a bed of clay which is 

 found in places above the limestone. The clay has been rendered 

 columnar, and the limestone has been marmorized. 



New-Bridge S ill (PL XIX).— At New Bridge, about 1 mile west 

 of Ashford-in-the-Water, on the road from Ashford to Taddington 

 and Buxton, a fine exposure of igneous rock about 50 feet thick is 

 seen on the left bank of the Biver Wye. The upper 30 feet con- 

 sist of a slaggy, vesicular, and amygdaloidal lava, contemporaneous 

 with the thin cherty limestones above it. The limestone-beds 

 above the lava are not altered, and the upper few feet of the latter 

 contain decomposed pyrites. 



The lower 20 feet of the igneous mass exposed by the roadside 

 consist of a hard, compact, ophitic olivine-dolerite with spheroidal' 

 weathering, very similar in appearance to the coarser portions of the 

 Tideswell-Dale Sill. The base of the igneous rock is not seen at this 

 place, but a few hundred feet nearer Buxton the dolerite on both 

 sides of the river rests upon the limestone below it. I have been 

 unable to find any signs of marmorization in these limestones, which 

 contain layers and nodules of chert. 



Above the right bank of the river, below Great Shacklow Wood, 

 large blocks of coarse dolerite are seen in a field; and on the 

 opposite side of the valley are blocks of a similar rock in situ below 

 the lava-flow. Here the intrusive rock soon thins out, but the lava 

 above it may be traced northward, to a point about 800 feet east of 

 Brushfield Hough, where it crosses the river. I have been unable 

 to trace it farther, because of the scree on the hill-slope. A good 

 section of the lava is also seen on the right bank of the river near 

 the Saw-Mill, a short distance south of New Bridge. 



The lower parts of the igneous mass near New Bridge consist of 

 an ophitic olivine-dolerite, which is more or less altered. Nineteen 

 thin slices were examined under the microscope. The olivine is 

 replaced by the Potluck pseudomorph and by calcite, serpentine, 

 and other alteration-products. In some cases the augite and fel- 

 spars are quite fresh. 



The blocks in the field on the right bank of the Wye vary from an 



