Following my 2016 visit to the Isles of Scilly, I described some of the variations that exist within the Devensian till exposures on the islands. Some photos are published here:
I was quite convinced at the time that there are many different lithologies within this till, which we can label as "Scilly till", using the terminology of Prof James Scourse and others. In my QN article, published last year, I devoted some space to discussing the possible mechanisms by which the till deposits had been formed and laid down. Some appeared to be basal lodgement till with shear structures and other signs of "glacitectonic" stresses, suggesting deposition on the glacier bed; others seemed to be flowtills, subject to rapid movement and redeposition; and others seemed to be "normal" meltout tills let down from a glacier surface by ablation processes. In some cases it is difficult to home in on the precise depositional mechanics without very detailed fabric analyses. To make matters more complex, there is sometimes an interdigitation with glaciofluvial deposits or periglacial deposits including frost-shattered slope breccia. To make matters even more complex, we see signs of wind-blown materials as well, incorporated into till, and where the ice has advanced across old beach sediments rounded pebbles, sand and gravels will be incorporated as well. In other words, wholesale chaos -- familiar to anybody who has spent time in an active ice-wastage environment on a glacier margin.
The classic locality for the lodgement till referred to as "Scilly Till" is Bread and Cheese Cove, on St Martins island. This has been studied by a number of researchers, and described in detail. It has been referred to as the "type locality" -- but the section is rather messy, and I am not sure why the till from this one locality should be thought of as "authentic" Scilly Till while others are somehow not authentic! As I said in another post:
I had problems with the "Scilly Till" type locality at Bread and Cheese Cove since the till there is associated with glacigenic structures which are not all that widespread and since other till exposures elsewhere are perhaps more typical of the northern fringes of the islands. ............ I had problems with the "Tregarthen Gravel" and the "Hell Bay Gravel" labels since they did not seem to have consistent characteristics and since some exposures were not at all gravelly. The labels seemed to me to be surplus to requirements.