Sedimentary slate at Applethwaite Common

 In his book "Slate from Coniston", Alistair Cameron has a diagram showing three veins of slate stretching across the Lake District. The one that goes from Banniside to Brathay and finally to Longsleddale is said to be sedimentary slate, rather than volcanic. He says it is blue/black veined and didn't rive well so was used for flag stones. Here's the evidence. Now to look for the volcanic slates.

Light as a feather?

 

I was interested that my new litter picker has been given a minimum mass for picking up. The hunt is now on for objects less than 1 gram which are big enough to be manageable in the jaws.

Experiencing thermal stratification in Bassenthwaite Lake

 

I took a dip in the lake on a lovely sunny day. I was confidently told that the water temperature was 19 degrees Celsius. As it happened, the water was noticeably warm but if I reached down more than 30cm, I could feel a cold layer below. It's been my introduction to thermal stratification. There is some interesting physics about how density differences result in different convection cells emerging. Also, that wind is the mixer that makes the layering break down as autumn arrives. It has been very windy here this summer so I'm interested to note that the layering still seems to exist. 

Convection: Low Wax Knott miners' bothy

 We'd read the story about the murdered miner so we went in search of the hut ... and found it.

At first it could have been a sheep fold, but it has a fireplace, a chimney and roof slates are scattered around inside. 

Living in a house with central heating as a child, I never understood the ventilating effect of a chimney. As the fire burns, the air expands, becomes less dense and floats upwards, up the chimney. The departure of air reduces the pressure below because there are fewer particle collisions. This means that the air outside which is at atmospheric pressure can force its way in to equalise the pressures. The advantage is that this brings in more oxygen for the fire. The bothy is small; it would have been very cramped but the fire would have made it hot inside. Hot but draughty with the air being pulled in through the doorway and the cracks by convection.

Starting to think about types of granite

 

This diagram is from Wikipedia - see here for full attribution. I've got my head round the top triangle which deals with the minerals in granite. The Q at the top is Quartz. The A on the left stands for Alkaline feldspar minerals. Feldspars seem to be based on aluminium silicates but can have sodium or potassium in making them Alkaline feldspars. But some have calcium in, which is the Plagioclase feldspar P on the right. As you can see in the diagram, granites contain more alkaline that plagioclase in general and are 2/5 quartz. Potassium feldspar is pink. Looking at the picture in my last post, the pebble on the extreme right is very pink. The looks like it might be alkaline feldspar granite. If I can get my head round the types of granite, I am hoping to work out the original source of the pebbles.

Where do the different granite pebbles at Silloth come from?

 We found a selection of different granite pebbles at Silloth. The one on the left is definitely from Criffel.

This display board from Watchtree might give some clues. It shows ice sheet movements during the Ice Age. Southern Scotland looks the most likely source but Shap is also possible. Cr means where Criffel erratics have been found so would be the southern limit of that ice sheet - where it butted into the Lake District ice.

There is one other detail that I have mentioned before - longshore drift moves pebbles from north to south above St Bees head, but south to north below. This should mean that rocks from Ennerdale might make it to Silloth but not from Eskdale. I need samples of granite from lots of places to compare to the Silloth photographs.

Normal reaction at Dubbs Reservoir

 

The force that a surface exerts upwards on an object perpendicular to the surface has had a rebranding. It was the Normal reaction force. Now it is the Normal contact force. I've started referring to it as the normal reaction contact force. I've always said that "reaction" shows that it isn't there until an object is placed on the surface, but I suppose "contact" now shows that. It is an electromagnetic force because it is due to positive nuclei repelling as the push of the object on the surface tries to force the nuclei closer. Some people label the upwards arrow R as they have done here beside Dubbs Reservoir above Troutbeck. Other people label it N.