The local sandstones underlying the area - all termed collectively "millstone grit" gives the area its acid soil comprising the substance for the heather moorland, and soft water in the Carboniferous period 325 million years ago, was in a swampy area at around sea level with meandering river channels coming from the north.
The layers in the eroded bank faces of stream gullies in the area represent sea levels with various tides depositing different sorts of sediment. Over a long period of time the loose sediments were cemented and compacted into hard rock layers. Geological forces lifted and tilted the strata a little towards the south-east and produced many small fractures, or faults.
Since the end of the Carboniferous time there has been a tremendous amount of erosion and more than a thousand metres of the coal-bearing rocks have been completely removed from the area. More recently, during the last million years or so, Ice Age glaciers modified the shape of the Wharfe valley, deepening it, smoothing it and leaving behind glacial debris.
Flora includes lots of Grasses and Rushes, Heathers and, of course, Bracken. Wavy Hair-grass covers large patches of the highest parts, while the fluffy white tufts of Cotton grass mark the damper spots. The heather comes in three - Ling (Calluna vulgaris), being the most common, but there is also
Bell Heather (Erica cinerea), and Cross-leaved Heath (Erica tetralix), both with larger flowers. In amongst, and becoming commoner, is Crowberry (Empetrum nigrum), which looks very like the heathers. You can tell it by its shiny black berries. On the drier Heather areas you will find plenty of Bilberry (Vaccinium myrtillus). Least and last among the relatives of Heather you may find Cranberry (Vaccinium oxycoccus), though only in the wettest places. There are small amounts of hard to see rich yellow spikes of Bog Asphodel (Narthecium ossifragum), and, in a a very few places, Sundew
(Drosera rotundifolia), sticky and spotted with the flies it has caught. The small flowers of Tormentil (probably Tormentilla erecta), are everywhere. The lower slopes can be thickly covered with Bracken (Pteridium aquilinum). Among the other more interesting ferns is the attractive upland Lemon-scented Fern (Oreopteris limbosperma), and of course there are trees - Birch, (probably Betula pendula and Betula pubescens), Rowan (Sorbus aucuparia), Hawthorn (Crataegus monogyna), Wild Rose (Rosa acicularis), Elder (Sambucus nigra), Bramble (probably Blackberry - Rubus fruticosus), Holly (Ilex aquifolium) and (some plantations) of Pine (Pinus sylvestris).Birds include Merlin (Falco columbarius), Short–eared Owl (Asio flammeus) and Golden Plover (Pluvialis apricaria), Red Grouse (Lagopus lagopus), Meadow Pipit (Anthus pratensis), Common Sandpiper (Actitis hypoleucos), Dunlin (Calidris alpina schinzii), Twite (Carduelis flavirostris), Snipe (Gallinago gallinago), Wheatear (Oenanthe oenanthe), Whinchat (Saxicola rubetra), Redshank (Tringa totanus), Ring Ouzel (Turdus torquatus), Curlew (Numenius arquata) and Lapwing (Vanellus vanellus), Cuckoo (Cuculus canorus), Wheatear (Oenanthe oenanthe), Nuthatch (Sitta europaea), Treecreeper (Certhia familiaris), Blackbird (Turdus merula), Song Thrush (Turdus philomelos), Chiffchaff (Phylloscopus collybita), Fieldfare (Turdus pilaris), Redwing (Turdus iliacus), Wren (Troglodytes troglodytes), Robin (Erithacus rubecula). Hawking for insects, there are plenty of Swallows (Hirundo rustica), Swifts (Apus apus), and House Martins (Delichon urbica), while Carrion Crows (Corvus corone), Jackdaws (Corvus monedula) and Rooks (Corvus frugilegus) are often on the wing looking for morsels. Kestrels (Falco tinnunculus), are distinctive, hovering on the wind..
Other fauna: Lizards, Frogs and Toads may be found and Green Hairstreak Butterflies (Callophrys rubi), whose caterpillars feed on the young Bilberry shoots, are most often seen.
Geology:The rocks of the Ilkley area are Upper Carboniferous (Kinderscoutian), so they are about 320 million years old. These rocks were laid down in deltas on the edge of a large continent, with mountains to the north and south. Sands and muds were deposited by rivers in shallow water. Because the continent was close to the equator, the climate was warm and wet so that tropical rain forest flourished. Dead plant material became trapped in stagnant swamps between river channels. Over geological time it was buried by muds and sands as the rivers in the delta changed position and built up more deposits. The water, oxygen and hydrogen were driven out of the plant remains, leaving only the carbon in coal seams. After the sediments were formed close to sea-level, they were buried by hundreds of metres of sediment and compressed. As the sea water was squeezed out, it carried minerals which cemented the sand and mud grains together to make rocks called sandstones and mudstones (shales).
The rocks were tilted into a large north-south trending fold, called the Pennine anticline, shortly after they were formed. However, the rocks in the Skipton area were also folded into east-west trending folds, probably because of the effect of older rocks of the Yorkshire Dales, which formed a resistant block bounded by the Craven Faults, which lie only a short distance north of Ilkley. The sandstone forming the Cow and Calf Rocks is called the Addingham Edge Grit. Higher up on Ilkley Moor are other sandstone beds, such as the High Moor Sandstone and the Doubler Stones Sandstone, which were deposited after the Addingham Edge Grit and therefore lie above it. All the sandstone beds vary in thickness and probably represent flood deposits in the delta area. Between the sandstone beds lie beds of mudstone (shales) which were deposited in marshes or swamps between the rivers on the delta. The pale grey mudstones sometimes contain fresh-water shells. During the Carboniferous period the sea-level changed regularly, because of glaciations in the southern hemisphere. Therefore the delta was sometimes drowned by sea-water which meant that dark mudstones were deposited above the delta sediments. These marine bands contain marine goniatite and bivalve fossils which can be found in some local mudstones. Because this change in sea-level happened regularly there are many alternations of sandstone and mudstone in West Yorkshire’s Carboniferous rocks. Because of later plate movements, the rocks here have been tilted to the south at a gentle angle, which results in the steep northern slope of Ilkley Moor, which overlooks the Wharfe valley.
Cross section to show the geology of the Cow and Calf Rocks, Ilkley
Sandstone is shown in yellow and is Addingham Edge Grit. Mudstones are shown without colour, underneath the sandstone. North is to the right and obviously South to the left.
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