Seven of us met for a shorter afternoon session to look at Carboniferous rocks in the northern part of the Craven Basin, visible in a small quarry near Bell Busk.

Much of the Yorkshire Dales lies on the Askrigg Block, a large block of granite that underlies the rocks and causes uplift of later rocks. The Craven Basin lies south of the Block and is separated from it by various faults, including the Mid Craven Fault.  During the earlier Carboniferous time the Block was covered  by a shallow warm tropical sea and Limestone formed. At the same time the Basin was filled by a deeper sea with rivers to the north draining into it and depositing mud. Between the Block and the Basin were shelf or ramp areas, slopes thus giving shallower areas of sea where muddy limestone could accrue. Sometimes tectonic activity would cause landslides on the shelves.

A track from the Aire bridge in Bell Busk leads up to Haw Crag quarry, the walls of the track are of limestone rocks often containing fossils of coral, found in the warm shallow seas. 

From above the quarry there is an excellent view to the north of the Cracoe Reef Knolls, formed on shelves in the warm seas on the Block and containing lots of fossil of shelly creatures.

To the west Malham Cove could be made out and the change from green grassy vegetation to brown rougher vegetation signalling the approximate line of the Mid Craven Fault. Looking to the south in the distance was a high point in the Basin, Pendle Hill but nearer to were drumlin hills, mounds of glacial till left by a retreating glacier.   

Within the quarry were two exposed faces of rock, lots of large to very large boulders jumbled up but in one area over-lying even larger blocks of vertically bedded (layered) rock which had clearly been upturned by incredible forces. The big boulder bed or conglomerate is known as the Haw Crag Boulder Bed and has been an SSI since 1954 as deemed significant geologically. The vertically bedded rocks are Hetton Beck Limestone.

The question remains how did these rocks get here in this disorder? One theory is as suggested above an avalanche, or turbidite, falling down the shelf or ramp. 

Smaller horizontal beds of rock were seen below the level of the above, all looking sedate and in their correct orientation, we concluded these were beds of the lower Thornton Limestone laid down before some of the above activity. 

A fascinating view of past environments, while also seeing the wider views of the local geological setting.

Leader Josephine Drake

Photos Ann Shaw J Drake