YORKSHIRE NATURALISTS AT GORMIRE AND THIRKLEBY. 



241 



beds. According to the Government Survey, the line of the northern 

 fault is very clear to the south of Byland Abbey, where the soft sand- 

 stones of the Estuarine series and the black Kimeridge shales are 

 seen within a short distance of each other on either side. To the 

 south of Kilburn the jet shales of the Lias are thrown against the 

 Upper Calcareous Grit, and judging from the thickness of strata 

 removed, the throw of the fault at this spot cannot be much less than 

 1,000 feet. At Thirkleby the Rhoetic beds are on the same level as 

 the Gray Limestone of the Lower Oolites. Another effect of these 

 great faults has been to shift the outcrop of the various beds ; thus, 

 for instance, the Rhoetic beds and Lower Lias which should be 

 south of Thirkleby, are found some miles to the westward, on the 

 west of Topcliffe. The time at disposal was too brief to allow of 

 many fossils being found, but Mr. Chadwick secured good specimens 

 of Beleuinites ahbreviatus and Gryphcea bilobata. The detachment 

 which investigated Gormire Lake and its vicinity reported in similar 

 terms on the strata they had seen. The origin of this lake has been 

 said by various writers to be due to a landslip, but this is a debatable 

 point. As Mr. Addison remarked, the lake is underlaid by some soft 

 shaly beds, and possibly, as he suggests, the subsidence, instead of 

 slipping of the rocks, may have originated it. The lake is encom- 

 passed by higher ground, so that it is a basin without any visible 

 outlet for the water, but by means of swallow-holes on the side next 

 to White Mare Cliff, the surplus water is supposed to be carried for 

 several miles till it joins the river Rye. Still, it must be remembered 

 that where harder rocks overlie clays or shales, landslips are common, 

 and these occurrences have, from this cause, been numerous in the 

 , Oolitic and Chalk hills. Thus, when the soHd rocks slipped over the 

 shales or clays, the latter, being exposed, would present an imper- 

 vious basin for the accumulation of water from the mountain springs, 

 and the talus or debris on the sides would dam up any outlet. It 

 should be stated that the geologists were much indebted to the 

 Rev. Frederic Addison, M.x\,, of Thirsk, for the ample and valuable 

 information he so readily supplied. It may be suggested that a 

 practical investigation into the origin of Gormire Lake would be 

 good and useful v/ork for the Thirsk Natural History Society. 



For the Section for Micro-Zoology and Micro-Botany, its 

 secretary, Mr. J. M. Kirk, of Doncaster, reported that Floscularia 

 corniita^ Stefitor inulleri, Milnesiwn tardi^rada^ Actinophrys sol, and 

 Ainceha diffluens (large) were found in Gormire Lake. After long 

 examination, nothing else was found but such as occur in any pond 

 at this time of the year. The water was crowded with the commoner 

 diatoms. 



Aug. 1887. 



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