Cow Pot limestone beds

[hannahb]

Yesterday whilst shivering waiting for something just beneath the climb & awkward tube at the bottom of the Cow Pot shakehole, I noticed that there are two distinct beds of limestone at that location. The lower one is paler and more creamy coloured; the upper one is darker and more grey coloured.

Does anyone know why, or have any references to literature about the different limestones in that area?

Ta.

 

[Pitlamp]

Sounds like it's potentially (but not necessarily) porcellanous limestone.

The best known one is that seen in GG Main Chamber (and much of the system) but there are others within the Great Scar Limestone sequence.

Have you got a sample? If so,on a freshly broken surface look for a dull texture with an absence of crystals (no obvious sparkling, like porcelein). Also a tendency towards conchoidal (shell like) fracture.

Or you could try the "Dick Glover Lick Test". If you lick a freshly broken surface (I kid you not) Dick Glover always maintained that porcellanous limestone will not change colour whereas normal sparry limestone will.

Without checking (in the middle of cooking as I type) you may find some information on the location of porcellanous beds in the Casterton area caves in the Waltham / Lowe book Caves & Karst of the Yorkshire Dales. Best to be aware that it's not only porcellanous limestone which can weather to a distinct whitish shade. This is why it's important to look at a freshly broken sample.

This picture shows a sample with normal sparry limestone at the top and porcellanous limestone at the bottom, for comparison. Zoom in to see the detail. Hope this helps.

 

[Cantclimbtom]

The GG porcellanous bands aren't thought to get that far. I have a book on the topic, will try to dig it out...

 

[langcliffe]

The GG porcellanous bands aren't thought to get that far. I have a book on the topic, will try to dig it out...

I suspect that @hannahb's observation was at too high a horizon for the Porcellanous Band. Dick Glover claimed to have identified it in Ease Gill Kirk.

 

[Pitlamp]

Yep: "The best known one is that seen in GG Main Chamber (and much of the system) but there are others within the Great Scar Limestone sequence.". If Hannah's pale bed is porcellanous, I agree it's likely to be one of these "others".

I've scoured Ease Gill Kirk for Dick Glover's porcellanous bed and wasn't convinced by any of the likely looking bedrock exposires. But I did find a loose block on the ground which was certainly PB. So it must be lurking somewhere around there.

I believe it's exposd in Pegleg Pot (which is a bit further up Ease Gill, so the exposure is underground rather than on the surface).

 

[Cantclimbtom]

I dug out "Limestones and Caves of Northwest England" (c) BCRA 1974 edited by A.C. Waltham with a section on "Development of the Caves of Casterton Fell" by P. Ashmead. But it's a bit technical for me and assumes a greater familiarity of the area than I have so apologies if I've misunderstood and quoting irrelevant text.

As far as I half misunderstand it, there's no porcellanous band to look for but there are a couple of marker bands of different limestone with fossils to watch for in particular the Cyritina Septosa band (according to some Googling) is a light grey very fossiliferous limestone containing remnants of brachiopods D. Septosa and Chonetes papilionacea.

Or.. I could be leading you astray

I'm very glad I went rummaging in that book because it was given to me by my now very elderly uncle who was an avid caver in the late 50s late 60s (UMIST and Stockport) and he made some vague mention about a note or two in the book but a cursory check before hadn't revealed any and I'd forgotten about it. But looking for this I've started seeing pencil notes he'd written for me, including Easter Grotto, Easgill. Now I understand what he's on about and I'll need to make a trip there some time.

Please see attached pic that's the most relevant section here?

 

[langcliffe]

As far as I half misunderstand it, there's no porcellanous band to look for but

it's there to look for, it's just that it hadn't been identified at that time. There has since been some evidence found for its presence, but not necessarily conclusive.