26 SCIENTIFIC SURVEY OF YORK AND DISTRICT 



the last occurring on deep peat. Changes seen in the vegetation are 

 closely related to the glacial history of the area ; in parts formerly occupied 

 by the glacier lakes bracken is conspicuous, also on the moorland slopes 

 of the valleys. The moist overflow channels are occupied by peat, 

 with an abundance of cottongrass, rushes and sedges, and make a marked 

 contrast with the surrounding heather moor. Plantations of conifers 

 form a zone along the lower margin of the moorland, but afforestation of 

 the heather moor, as at Allerston Moor, is seriously hindered by the 

 presence of moor pan. 



Draining these moors to the south are the tributaries of the Derwent 

 which form a series of well-wooded and picturesque dales, including 

 Forge Valley, Newtondale, Rosedale, Farndale, Bransdale, and Bilsdale, 

 each with an interesting flora. In Forge Valley and in the neighbourhood 

 of Hackness occur Helleborus viridis, Aquilegia vulgaris, Actcea spicata, 

 Cornus suecica, Afropa Belladonna, Myrica Gale, Spiranthes autumnalis, 

 Epipactis ensifolia, Maianthemum bifoUiitn, Osmunda regalis and Equisetum 

 hyemale. At the head of Newtondale is a small branch glen, the Hole 

 of Horcum, noted as a station for Cornus suecica, one of the few montane 

 plants found in the east but absent from the western calcareous dales. 

 Other plants of interest in Newtondale, in addition to some above-men- 

 tioned, are TroUius europceus. Astragalus hypoglottis, Carduus eriophorus, 

 Inula Helenium, Salvia verbenaca, Neottia nidus-avis, Habenaria albida, 

 Ophrys mucifera, Gagea lutea and Convallaria majalis. 



In Ryedale and the neighbourhood of Helmsley a similar flora occurs, 

 and there is one of the stations of the lady's slipper orchid. The Vale 

 of Pickering is a flat low- lying tract, extending from the coast inland 

 for thirty miles. It is intersected by streams from the dales and contains 

 many carrs and marsh lands. 



The Howardian Hills comprise two narrow parallel terraces which 

 extend from the calcareous hills eastwards to the Derwent and are situated 

 on the south-west of the Vale of Pickering and separate it from the 

 Vale of York. The northern terrace is composed of calcareous beds 

 of the Lower Oolite ; the southern one of Lower Oolite based on Lias. 

 This tract furnishes a great variety of surface and vegetation — moorland, 

 woodland, parkland (including Castle Howard), also Terrington Carr, 

 a well-known heathery swamp, and though there are no montane species, 

 there are as many of the rarer species to be found within an equal area 

 as anywhere in Yorkshire excepting Upper Teesdale. 



The Hambleton Hills form a calcareous range with an elevation of 

 i,ioo ft. At Boltby Scar, Whitestone Cliff and Roulston Scar are 

 three fine precipices formed of calcareous grit. Whitestone Cliff is 

 a perpendicular clifT loo ft. deep, the base of which is covered with 

 fallen debris from the summit. At the foot of this cliff is Lake Gormire, 

 the largest tarn of the East Yorkshire Hills. These grits rest upon 

 Oxford Clay, rendering them unstable, and a landslip thus produced 

 closed one end of what was probably a glacial lake overflow channel 

 and obstructed the drainage. Except for the drainage from the hill 

 bank no streams flow into it, and its waters are mainly supplied by 

 rain and diminished by evaporation. The following plants occur here 



