Geology and geomorphology

On this page: I got my degree in geology, and have kept an amateur interest in it ever since. This page records some of my observations on the subject as it relates to the pasture.

Geology

photo of 'head' - flints in clay matrixThe soil is flinty in places and reasonable loam in others; the only exposure of the bedrock is in the banks and bed of the stream. Here, there is a cover of 'head' - poorly sorted sharp flints and yellow-brown sandy clay of (probably Eocene) origin, over the greenish or yellowish sandy clays of the Cretaceous upper greensand. There are two distinct kinds: one has a warm brown matrix as shown right, and the other (which I think underlies the first in places) has a more stratified, clayey yellow matrix, as shown below left. Although the IGS map shows the drift as 'clay with flints etc.', here it isn't the classic clay-with-flints, which comprises rounded blackened flints - ours are not blackened and mostly shattered and sharp.photo of greensand exposed in stream bank I guess most of the flints and chert are derived from the chalk which has now weathered away, and the matrix is mostly from greensand. If anyone knows better, please let me know!

There aren't many exposures in the immediate locale, but of course the shore at Lyme, only a mile away, has a famous succession of lower Jurassic shales and limestone (shown in the links section). Lying unconformably on these is the greensand, which makes up a lot of the jumbled strata of the famous landslips of the Undercliff, and the prominent yellow tops of the local hills like the Spittles, Golden Cap and Thorncombe Beacon. It can also be seen in Shapwick Quarry, which provides ballast and roadstone.

photo of Chimney Rock - a middle chalk exposureThe greensand is overlain by chalk - Chimney Rock in nearby Ware is comprised of middle chalk - a rather dirty greyish rock with abundant chert seams. (The rock is so-called because there is a small stack at the top, now overgrown. It is said that nonconformist preachers used it as an open-air pulpit - I'm not sure how many people could have gathered around such a precipitous place. It's only one of a number of chalk bluffs along the Undercliff.)

Links to other geology resources

photo of Jurassic rocks at Lyme RegisThere is more information about the local coastal geology on Graeme Caselton's link to external site Jurassic Cliffs page. You might also want to look at link to external site Dr Ian West's excellent page, where you can choose several field guides in the Lyme Regis area.

I have a page on local landslips, and another on fossils at Lyme.

go to topOur stream

We are lucky to have a stream from which we are permitted to take water for animals. (My DIY page has some hints if you feel like putting your own trough in cheaply.)

photo of stream meandering between narrow banksIn winter, it's largely fed by run-off from the roads and fields (of which there is a huge amount, because most of the higher fields are winter cereals, and get washed out in wet weather. We have the dubious privilege of getting lots of silt, and probably fertiliser, belonging to someone else.) After a heavy rainstorm, the stream is transformed into a foaming yellow torrent bearing all before it (well, branches and quite large rocks, anyway). photo of stream in floodWhen the water has subsided, the stream-bed has usually been entirely reshaped, with new potholes and runnels, and fresh surfaces exposed on the outer corners of the bends.

In the summer, the upper course is dry, but halfway down, there is a mysterious, still pool which always has a steady trickle of water leaving it. The spring appears to be at the upper boundary of the greensand, and hasn't let us down yet even in the driest summer. There are also the remains of some clay land drains appearing in places in the banks - at one time, they must have been buried metres below the surface, collecting water from who knows where.

photo of stream in open valleyThe valley has a variable profile, but is obviously over-sized for the stream now. The stream has cut quite steep-sided channels in places (including the big hole of which a neighbour memorably said, "Bloody hell, there's a hole big enough to hide a Land Rover under those brambles" - fortunately before he was about to walk into the briar patch). In other places, it runs over the surface with no real course: mostly in the upper reaches where the flow is seasonal. You can see where the water has been by the way the grass is combed in one direction, and tree-roots are exposed.

Terraces

photo of terraced slopeThe upper slopes of the hill are mostly terraced: these small ridges and flats are about 1m in amplitude, and are caused by soil creep down the hill. Keeping stock in the field accentuates them, because the natural tendency of any sensible animal (and horses too) is to walk on the level across the slope, which accentuates the flats.

(A glossary used by soil scientists tells me the approved term is 'terracettes', but this sounds too camp for words! I imagine Sandy and Jules perched on them sipping G&T and eating dainty cucumber sandwiches.)