632 liEPORT — 1881. 



augment the amount of evaporation. Hence, if -with a steady heat-supply there 

 be a given amount of evaporation, fluctuations in that supply will in like manner aug- 

 ment that amount. Or it fluctuations already exist, an increase in their extent -will 

 still further augment the amount. But increased eccentricit)' can increase the difler- 

 ences in the rates of heat-supply; also evaporation is equal to precipitation. There- 

 fore under increased eccentricity the annual snowfall may be augmented without any 

 accompanying increase of annual melting. Thus an uncompensated annual surplus 

 of snow may be produced which will pccumulate. The possible increase for fluc- 

 tuations of a probable amount is calculated, and found to be appreciable and con- 

 siderable. 



11. On the Discovery of Goal-Measures nnder Neiv Red Sandstone, and on the 

 so-called Permian lioclis of St. Helen's, Lancashire} By A. Strahan, 

 M.A., F.G.S., Geological Survey of England and Wales. 



The Trias has been penetrated, during the last few years, by three colliery 

 shafts and three boreholes in the district bordering the St. Helen's and Wigan coal- 

 fields on the south. It was thinner than might have been expected, while the 

 Permian formation was altogether absent. This latter formation was believed to 

 underlie the Trias, but to be overlapped, so as not to appear at the surface, except- 

 ing at St. Helen's Junction, where a marl-bed, and a soft sandstone beneath it, 30 

 and 90 feet thick respectively, and supposed by Messrs. Binney and Hull to be 

 Permian Marl and Lower Permian Sandstone, were found in a quarry and a well. 



The Bold Hall Colliery shaft, at about 1 mile from the outcrop of supposed 

 Permian rocks, proved the shale to maintain its thickness, but the sandstone to 

 be 57 feet inches only. The Coal-Measures were entered at 186 feet, and pene- 

 trated to a depth of 1,800 feet from the surface, when the Florida Mine was met 

 with. The red staining, due to the Trias, extended to a depth of 365 feet in the 

 Coal-Measures. 



The Collins Green Colliery shafts, at the same distance from the boundary of 

 the Trias, but three-quarters of a mile north-east of Bold Hall Colliery, proved 

 the shale to be 22 feet, and the sandstone 44 feet in thickness. The latter con- 

 tained spherical concretions of iron pyrites, binding the grains of sand in their 

 original position in the planes of bedding. The Coal-Measures were entered at 

 310 feet 10 inches, and penetrated to the Florida Mine, at 1,067 feet 7 inches 

 from surface. They were red for 152 feet. The dip of the so-called Permian was 

 to the south-east at C°, that of the Coal-Measures at 10°. 



The Ilaj'dock Colliery shafts (Lyme Pits), at the same distnnce from the 

 boundary of the Trias, are 1 mile north-east of Collins Green. The shale and 

 sandstone had diminished here to 9 feet and 7^ feet respectively. The Coal- 

 Measures were penetrated to a depth of 97 feet 2 inches, or 413 feet 3 inches from 

 surface. In the shafts of this and the Collins Green Collier}', the unconformity 

 of the red sandstone and the Coal-Measures was clearly visible. 



The above sections show that the so-called Permian Marl and Sandstone thin 

 out gradually from west to east, the lower thinning out first, and not the upper, 

 as would have been the case if they had been unconformably overlapped by the 

 overlying beds. They thin out to the south also, as proved by a borehole near 

 Farnworth, 3 miles south of St. Helen's .lunction, which, after penetrating 124 feet 

 of yellow and white sandstone, passed through 3 feet of red and white clay, 3 feet 

 of red sandstone, and entered purple marls with bands of limestone, belonging to 

 the Coal-Measures. 



The so-called Permian Beds, though unconformable to the Coal-Measures, are 

 quite conformable to the Trias, and are overlapped in consequence of an attenua- 

 tion in themselves, and not through having suffered denudation before the Trias 

 was deposited upon them. Considering also their lithological similarity to the 

 Trias, it seems that they should be classed with this formation, rather than with 

 the Permian. 



' Published iiiextenso in the Geological Magazine for October 1881. 



