Rock sequences


Geological Conservation Review (GCR) sites are selected for, and grouped according to, GCR blocks, which are site-selection categories for nationally important Earth science sites.  There are around 100 'blocks' and about 3,000 GCR sites in Britain.  Each 'block' represents a particular geological age or Earth science theme, such as Marine Permian Stratigraphy, Jurassic–Cretaceous Reptilia, Caledonian Igneous Rocks and Quaternary of Scotland.
For the most part, sedimentary rock sequence sites are classified according either to their stratigraphical age (Stage, Period) or to a range of stratigraphical ages (e.g. Caradoc–Ashgill block).  Blocks for some stratigraphical ages, however, were defined not purely by age, but also by geographical area or environmental setting where there were significant variations in rocks across Britain formed at the same time.  This is why there are two blocks for the Devonian Period; one for marine rocks and one for non-marine rocks.
It is not possible in every case to define the stratigraphy GCR blocks by stratigraphical age.  For example, where fossils are rare or absent it is difficult to locate the boundary between different geological ages.  Such units are named after the geographical localities where they were defined, for example, the Wealden Group, which consists of mudstone, shale and sandstone which only occur in south-east England.
Most invertebrate fossils (e.g. trilobites, echinoderms, ammonites and other molluscs) are also addressed within the stratigraphical blocks, because these fossils are widely used in correlating rock strata.  However, because of the relative rarity of fossils such as reptiles, fish, mammals, birds, terrestrial plants, insects and other arthropods (excluding trilobites) these are covered in separate palaeontological (fossil) blocks.

Summary statistics

  A/SSSI Total
Favourable condition 83% 83%
Main monitoring coverage E, S, NI  
Reported assessments 859 859
Completeness of assessments approx.80%  
Distribution of features   UK

Number of assessments reported by country and site type

England 725
Scotland 112
Wales 0
Northern Ireland 22
United Kingdom 859

SSSI features

List of SSSI and ASSI interest features in this reporting category

Interest feature name  
Formal name Informal name No. of assessments reported
Aalenian - Bajocian Aalenian - Bajocian 51
Aptian - Albian Aptian - Albian 29
Arenig - Llanvirn Arenig - Llanvirn 10
Arenig - Tremadoc Arenig - Tremadoc 3
Bathonian Bathonian 46
Berriasian, Valanginian, Hauterivian, Barremian Berriasian, Valanginian, Hauterivian, Barremian 11
Callovian Callovian 14
Cambrian Cambrian 9
Cambrian - Tremadoc Cambrian - Tremadoc 2
Caradoc - Ashgill Caradoc - Ashgill 23
Carboniferous stratigraphy Carboniferous stratigraphy 9
Cenomanian, Turonian, Senonian, Maastrichtian Cenomanian - Maastrichtian 2
Cenomanian, Turonian, Senonian, Maastrichtian Cenomanian, Turonian, Senonian, Maastrichtian 36
Cretaceous stratigraphy Dunnaglea - Larrybane 1
Cretaceous stratigraphy Cretaceous stratigraphy 2
Dinantian of Devon & Cornwall Dinantian of Devon & Cornwall 9
Dinantian of northern England & north Wales Dinantian of northern England & north Wales 55
Dinantian of Scotland Dinantian of Scotland 1
Dinantian of southern England & south Wales Dinantian of southern England & south Wales 11
Hettangian, Sinemurian and Pliensbachian Hettangian, Sinemurian and Pliensbachian 26
Jurassic stratigraphy Jurassic stratigraphy 2
Kimmeridgian Kimmeridgian 13
Llandeilo Llandeilo 3
Llandovery Llandovery 19
Lower Carboniferous [Dinantian - Namurian (part)] Lower Carboniferous [Dinantian - Namurian (part)] 24
Ludlow Ludlow 21
Marine Devonian Marine Devonian 44
Marine Permian Marine Permian 24
Namurian of England & Wales Namurian of England & Wales 37
Neogene (Pliocene) Neogene (Pliocene) 16
Non-marine Devonian Non-marine Devonian 24
Ordovician stratigraphy Ordovician stratigraphy 3
Oxfordian Oxfordian 31
Palaeogene Palaeogene 26
Permian - Triassic Permian - Triassic 32
Permian - Triassic (red beds) Permian - Triassic (red beds) 10
Permian stratigraphy Permian stratigraphy 1
Portlandian - Berriasian Portlandian - Berriasian 17
Precambrian of England & Wales Precambrian of England & Wales 11
Rhaetian Rhaetian 9
Silurian stratigraphy Silurian stratigraphy 2
Toarcian Toarcian 15
Tremadoc Tremadoc 3
Triassic stratigraphy Triassic stratigraphy 2
Upper Carboniferous [Namurian (part) - Westphalian] Upper Carboniferous [Namurian (part) - Westphalian] 7
Wealden Wealden 36
Wenlock Wenlock 29
Westphalian Westphalian 48
This list has not been fully standardised at a UK level yet. It is intended to show the principal constituent "feature types" for this reporting category.

Maps - distribution

UK distibution of reported interest features

Distribution of reported interest features.

Map showing the locations of the 10km squares in which at least one condition assessment has been reported. It does not show features that have not yet been assessed.


Maps - SSSI

Current condition of SSSI/ASSI features Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
Current condition of SSSI/ASSI features
Distribution of SSSI/ASSI features showing assessments of favourability (where unfavourable-recovering is counted as unfavourable).
Condition of SSSI/ASSI features, with those currently reported as unfavourable-recovering shown as favourable
The implication of the unfavourable-recovering condition assessments is that at some point in the future these features should become favourable. This map shows the effect of that recovery by counting the favourable and unfavourable-recovering assessments together.


IMPORTANT NOTE: we do not have information on the timescale of the predicted recovery, which may be influenced by many past, natural and human related factors. A sustained sympathetic management regime is more likely to result in favourable condition being attained.

Key: Proportion of assessed features on 10km squares that are favourable:

SSSI map legend - Proportion of assessed features on 10km squares that are favourable


Details of how these maps were produced


Condition summary

Reporting category condition summary on SSSI/ASSI sites

This lists the 10 different condition assessments and presents a bar chart showing the number of features within the SSSI series. Note that we are unable to estimate the total number of SSSI/ASSI features because we do not have an overall list of notified interest features for these designations.


NB favourable unclassified and unfavourable unclassified have been used in this first six year cycle to get around difficulties in identifying trends in condition as common standards monitoring is implemented. It is expected that these categories will not be used for subsequent assessments of a feature.


Condition assessment - SSSI features

The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories
The number and proportion of assessments for SSSI/ASSI interest features falling into each of the condition categories. Note that the �unfavourable� category includes all reports of unfavourable condition except �unfavourable recovering� which is shown as a separate segment.

Adverse activities

The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature
The number of interest features where an activity has been reported as being implicated in the "unfavourable" condition of a feature. More than one adverse activity may be reported for each feature.

Management measures

The measures summary bar chart lists the management measures relevant to the reporting category
For each "measure" the chart shows the number of interest features where that measure has been taken on a site to improve or maintain the condition of an interest feature. More than one measure may be reported for each feature assessed.


Sites with rock sequences are numerically the greatest in the A/SSSI series for geological sites.  The assessments made represent about 80% of sites with stratigraphical features.  83% of features reported are in favourable condition, with a further 2% of features in unfavourable-recovering condition.  This level of favourable condition is below the average for geological features, but well above the average for all features combined.
Data on the reasons for sites being in unfavourable condition, or measures helping them to become or remain favourable, were reported for only a subset of the features assessed.  However, the principal reason reported for sites being unfavourable is that the feature is obscured.  Many sites have a management agreement in place; this will include measures to keep the feature exposed.