THE CORALLXAN ROCKS OE ENGLAND. 345 



the Trigonia-heda of Pickering, occupies the channel of the stream at 

 the ford on the old road between Kirkby Moorside and Helmshw. 



Passing still to the west, we find these Lower Limestones of great 

 importance between the gorges of Hodge beck and Eiccal dale. Some 

 of these quarries present us with examples of the silicification of the 

 whole of the beds composing them. Sections of the oolitic grains 

 show the concentric structure; and the}' are coloured brown or black 

 by the presence of carbon, as in ordinary flint, with a trace pro- 

 bably of iron. They are imbedded in a white matrix, which is 

 almost pure silex, while every crack, exposed surface, or fossil is 

 covered with the same substance in the form of beekite. These 

 features are well seen in quarries behind Skiplam wood and Oxclose 

 wood. 



The Middle Calcareous Grit here varies as much as it is seen to 

 do towards the east, being a yellow sandstone in the region imme- 

 diately north of Marston, but in the sides of Eiccal dale so compact 

 and calcareous as to be with difficulty distinguished in small open- 

 ings from the limestones above and below, except by its being non- 

 oolitic. We thus see throughout this range that this Middle Grit 

 appears in the form of isolated sandbanks, its maxima being near 

 Pickering and Kirkby Moorside, its minima near Thornton and Eiccal 

 dale. 



The Upper Limestones and Upper Calcareous Grit. — As we enter 

 the Pickering district from the east, along the edge of the vale, 

 we first meet with tho Upper Limestones in a small quarry just 

 west of Thornton, where the beds are dipping S.W., as we should 

 expect ; but a little further on we see a very good seotion at the 

 end of a dry gash called Howl dale, about halfway to Pickering, 

 where the dip is southerly and moderate. 



Quarry west of Hagg House, in the Upper Limestone. 



Corresponding 



in Pickering Section. ft. in. 



a. 1. Upper Calcareous Grit, very fossiliferous ... 6 



b. 2. Argillaceous marly layers 2 



d. 3. Dense ferruginous limestone in irregular 



lumps t> 



4. Oolite — few fossils 6 6 



e. 5. Dense and sometimes earthy limestones,with 



some oolitic granules — few fossils 12 



/. 6. Ckemnitzia-limestones to base of quarry. 



27 



With the exception of the oolite (4), all these beds have their 

 counterparts in the great Pickering section, though in very different 

 degrees and conditions of development. Excepting the fragment on 

 the Hackness outlier, this is the last place to the eastward where 

 the Upper Calcareous Grit is noted. It is also the most easterly 

 point in Yorkshire where there is any trace of the Florigemma-iag, 

 the richest and most interesting of all the subdivisions of the 

 Corallian Limestones. Here this is feebly represented by no. 3, 



