Geologically the western half of the island has underlying greenish-grey granodiorite, covered for the most part by a gritty, sandy, head of decomposing rocks and wind-blown loess. A central triangular band of diorite stretches across the island from Cachalière to Braye Bay and Corblets Bay, whilst the south-eastern half of the cliffs and the low eastern end of the island is overlain with a thick layer of the hard Alderney sandstone, which also covers the extreme edge of much of the northern coastline and forms all of the offshore reefs, stacks, islets and islands, stretching some 25 miles due west, from Le Cap de la Hague, on the Normandy coast to the Casquets. A large area of the northern and eastern sides is covered with windblown sand forming a permanent dune system stretching across the top of the lower part of the island from Braye Bay to Longis Bay and along the northern coast from Corblets and Saye Bays in the east to Tourgis Point at the NW end. At the western end, Platte Saline and the area immediately behind it, up to about the 60m. contour line, forms another ancient, permanent dune system. There is evidence of former raised beaches at the 8 and 18m levels in a number of spots along the N and NW sides and on the offshore islands; remnants of the time when these areas were underwater during the various ice-ages.
A number of small, spring-fed streams run down the narrow valleys spaced along the S & W coasts and down the fewer but wider north facing valleys. The largest of these streams, in Bonne Terre, nowhere exceeds 1m. in width and about 20-30 cms. in depth.
The soil is generally neutral to slightly acid, except in many of the sandy parts, where crushed mollusc shells impart a degree of alkalinity and support calcicolous (lime-loving) species of plants and animals.
Please Note;
(a); An A4 map of the island, drawn by the author, showing the UTM grid numbers and names of most of the features, appears as the frontispiece of the printed version, or, as a full A4 size file in the CD version (File Alderne.jpg), which the user can print if required.
(b); A geological sketch map, also drawn by the author, is also included immediately below.
(c); 1. Throughout this part of the work the scientific names of plant and animal species will be given, in italics, following their common names, (where they have one), on the first occasion of their use. Thereafter only the common names will be used. Thus, in general, scientific names will only occur once in the index.
2. In general, only common names will be used in the Diary section.
3. A note on Protective Legislation for the Alderney flora, fauna and environment will be found in Appendix 1, at the end of the work.
Figure 1.
