﻿Yol. 64.] CAKBONIFEROUS LIMESTONE OF THE MIDLAND AEEA. 41 



a downthrow to the east of about 200 feet, has brought these 

 massive white limestones down to the level of the railway at Litton 

 Tunnel, and has thrown the lowest beds of the cherty-limestone 

 series into juxtaposition with the lower part of the toadstone, in 

 the cutting west of Litton Tunnel. 



The whole of the Carboniferous Limestone exposed in this section 

 is included in the DibunopJiyllitm- Zone, in which the three following 

 subzones are recognizable : — 



The Cyathaxonia-suhzone (D3) includes the limestone-and-shale 

 series which constitutes a passage into the overlying Pendleside 

 Shales, and at least 70 feet of the cherty-limestone series. 



The Lonsdalia-suhzone (D^) includes the remainder of the cherty- 

 limestone series. 



The Dibunopliyllum 0-subzone (D^) includes the whole of the 

 series below the upper toadstone, down to the base of the section. 

 [The massive limestones, about 120 feet thick, which lie between 

 the upper toadstone and the cherty limestone, are relatively unfossili- 

 ferous, and are not definitely assigned either to D^ or to D^.] 



The nature of the exposures at various horizons may be briefly 

 noted. 



Dg. — The beds of this subzone are well exposed in the railway- 

 cutting immediately east of Headstone Tunnel, west of Longstone 

 Station. 



Dg. — The highest levels exposed in D^ are seen on the slopes of 

 Monsal Dale, both immediately above the western mouth of Head- 

 stone Tunnel, and in White Cliff aud other adjacent exposures on the 

 north side of the dale. The main part of the cherty-limestone 

 series is exposed in the cuttings between Headstone Tunnel and 

 Cress brook Tunnel ; also at certain points on the northern side of 

 Monsal Dale ; and in several exposures on the hill over Cressbrook 

 Tunnel. The base of the series is seen at the western end of Cress- 

 brook Tunnel and at both ends of Litton Tunnel. The cuttings 

 immediately west of Litton Tunnel expose limestones very near the 

 base of the cherty series ; but the fault which has been already men- 

 tioned soon comes in, and thence onwards to Miller's-Dale Station 

 the cuttings lie in the upper toadstone and the massive limestone 

 underlying it(D^). The lowest beds of the cherty series are again 

 exposed on the slopes above the large quarry (Miller's-Dale Lime- 

 Works) south of the railway. The quarry itself exposes the massive 

 white limestones, immediately overlying the upper toadstone, which 

 may belong either to D^ or to D^. 



Excellent supplementary exposures of the ZonscZaZia-subzone are 

 afforded by the cliffs and rock-masses at ' Hob's House,' on the east 

 side of Monsal Dale, a short distance south of the railway-viaduct. 



D^. — The following are the best exposures of the limestones 

 between the two toadstones : — (1) A disused quarry on the south 



