A formation or geological formation is the fundamental unit of lithostratigraphy. A formation consists of a certain amount of rock strata that have a comparable lithology, facies or other similar properties. Formations are not defined by the thickness of their rock strata; the concept of formally defined layers or strata is central to the geologic discipline of stratigraphy. Groups of strata are divided into formations; the definition and recognition of formations allow geologists to correlate geologic strata across wide distances between outcrops and exposures of rock strata. Formations were at first described as the essential geologic time markers, based on their relative ages and the law of superposition; the divisions of the geological time scale were described and put in chronological order by the geologists and stratigraphers of the 18th and 19th centuries. The lithology of a rock is a description of its visible physical characteristics. Modern geology prefers to use lithology, that it an examination of the visible features of the component rocks, to identify discrete formations.

Geologic formations are divided into the broad categories of: sedimentary rock layers. Intrusive igneous rocks are not considered to be formations; the contrast in lithology between formations required to justify their establishment varies with the complexity of the geology of a region. Formations must be able to be delineated at the scale of geologic mapping practiced in the region. Geologic formations are named after the geographic area in which they were first described. Formations cannot be defined by any criteria other than primary lithology, it is useful to define biostratigraphic units on paleontological criteria, chronostratigraphic units on the age of the rocks, chemostratigraphic units on geochemical criteria. The term "formation" is used informally to refer to a specific grouping of rocks, such as those encountered within a certain depth range in an oil well "Formation" is used informally to describe the odd shapes that rocks acquire through erosional or depositional processes; such a formation is abandoned.

Some well-known cave formations include stalagmites. Geochronology – Science of determining the age of rocks and fossils List of rock formations – Links to Wikipedia articles about notable rock outcrops List of Chinese geological formations List of fossil sites – A table of worldwide localities notable for the presence of fossils

Castell Caer Seion is an Iron Age hillfort situated at the top of Conwy Mountain, in Conwy County, North Wales. It is unusual for the fact that the main fort contains a smaller, more defended fort, complete with its own distinct defences and entrance, with no obvious means of access between the two; the construction date of the original fort is still unknown, but recent excavations have revealed evidence of occupation as early as the 6th century BC, whilst the smaller fort can be dated with reasonable certainty to around the 4th century BC. Whilst the forts were constructed in different periods, archaeologists have uncovered evidence of concurrent occupation up until around the 2nd century BC; the larger fort contained around 50 roundhouses during its lifetime, whereas examinations of the smaller fort have turned up no more than six. The site was traditionally associated with Maelgwyn Gwynedd, but there is no evidence pointing to a 6th-century occupation; the fort and wider area beyond its boundaries have been said to retain significant archaeological potential, are protected by law as a scheduled ancient monument.

The fort is on the summit of a ridge of rhyolite at an altitude of 800 feet and is enclosed by a single rampart, with more complex works protecting a smaller fortified area at the western end. The northern side of the ridge is steep enough to offer a natural defence meaning that no outer wall was needed for the first phase of construction; the smaller fort was built inside the western margins of the larger fort sometime around the 4th century BC. The site has a commanding position overlooking Conwy Bay, is situated close to a major trackway that follows the coastal ridge; the total area of the fort is 7.5 acres, it is 326 metres long, at its widest measures around 95 metres from the southern ramparts to the cliffs on the northern boundary. Writing in Archaeologia Cambrensis, W. E. Griffiths and A. H. A. Hogg identify'Caer Seion' as the older and more genuine name of the hillfort, for which they cite evidence dating as far back as the 9th century; the alternative name'Castell Caer Lleion' seems to date to the late 17th century and came about due to a mistranslation.

Indeed,'Castell Caer' is somewhat of a tautology, translating into English as "Castle Fort". Because there is no standardised name for the site, it is referred to variously as'Caer Seion','Castell Caer Seion','Castell Caer Lleion','Castell Caer Leion' and'Conwy Mountain hillfort'. An antiquated name, no longer in popular use but recorded by John Leyland in his 1530s Itinerary in Wales, is'Sinnodune'. There have been three principal excavations at the site: first in 1906 and 1909 in 1951 and 1952, in 2008; the dearth of dateable finds meant that, until the early part of the 21st century, the dating of the site was inferential. Each excavation has revealed a little more about the site, with modern techniques enabling archaeologists to date the earliest known occupation of the fort to within 200 years; the first recorded excavations – carried out by Harold Picton and W. Bezant Lowe – were begun in 1906, before a delay caused them to abandon the project and resume it in 1909, their excavations revealed little, but they are the first to record finding sling stones at the site, they turned up a rubbing stone.

Bezant Lowe noted the possible existence of a semi-circular defence facing the entrance to the smaller fort. In one of the huts at the south-western end of the small fort they uncovered a stone floor, haphazard for the most part, but laid and fitted together at one side of the hut. Picton notes that there was no evidence of the floor being used as a hearth, but does not speculate further as to the nature of the feature. By far the most extensive of the excavations were those conducted on behalf of the Royal Commission on the Ancient and Historical Monuments of Wales. Most of what we now know about the site stems from these digs, carried out by W. E. Griffiths and A. H. A. Hogg, they concluded that the site showed two periods of fortification, both within the latter part of the pre-Roman Iron Age. Whilst we now know that the fort was occupied as early as the Early to Middle Iron Age, the archaeologists did note at the time that their evidence for dating was slight, they were the first to provide evidence that the two forts were designed to be used concurrently, based on the layout of the walls at the juncture of the two enclosures, speculate that the two separate enclosures were accessible to each other via some form of moveable ladder.

No direct evidence exists to support this, but Griffiths and Hogg thought it because of the existence of a level causeway leading through the eastern defensive ditch to the northern corner of the small enclosure, where there were no entrances. The third excavation was small in scale, but important for being able to offer definitive dating evidence pertaining to the occupation of the two forts, it was carried out by George Smith of the Gwynedd Archaeological Trust, on behalf of Cadw, with environmental reports by Astrid E. Caseldine and Catherine Griffiths from the University of Wales, they were inspired to carry out this undertaking because of a 1991 survey by the Snowdonia National Park Authority, which remarked that the 1956 excavation had identified charcoal-rich layers that could be targeted for future research. The excavati

The Missile Technology Control Regime is a multilateral export control regime. It is an informal political understanding among 35 member states that seek to limit the proliferation of missiles and missile technology; the regime was formed in 1987 by the G-7 industrialized countries. The MTCR seeks to limit the risks of proliferation of weapons of mass destruction by controlling exports of goods and technologies that could make a contribution to delivery systems for such weapons. In this context, the MTCR places particular focus on rockets and unmanned aerial vehicles capable of delivering a payload of at least 500 kg to a range of at least 300 km and on equipment and technology for such systems; the MTCR is not a treaty and does not impose any binding obligations on Partners. Rather, it is an informal political understanding among states that seek to limit the proliferation of missiles and missile technology; the Missile Technology Control Regime was established in April 1987 by the G7 countries: Canada, Germany, Japan, the United Kingdom, the United States of America.

The MTCR was created in order to curb the spread of unmanned delivery systems for nuclear weapons delivery systems that could carry a payload of 500 kg for a distance of 300 km. The MTCR applies to exports to other members as well as exports to non-members; however an "aide memoire" attached to the MTCR states that it does not supersede prior agreements, which NATO members argue allows the supply of Category 1 systems between NATO members. An example is the supply by the Unites States of Trident missiles to the United Kingdom for nuclear weapons delivery. At the annual meeting in Oslo on 29 June - 2 July 1992, chaired by Mr. Sten Lundbo, it was agreed to expand the scope of the MTCR to include nonproliferation of unmanned aerial vehicles for all weapons of mass destruction. Prohibited materials are divided into two Categories, which are outlined in the MTCR Equipment and Technology Annex. Membership has grown to 35 nations, with India joining on 27th of June 2016 adhering to the MTCR Guidelines unilaterally.

Since its establishment, the MTCR has been successful in helping to slow or stop several ballistic missile programs, according to the Arms Control Association: “Argentina and Iraq abandoned their joint Condor II ballistic missile program. Brazil and South Africa shelved or eliminated missile or space launch vehicle programs; some former Warsaw Pact countries, such as Poland and the Czech Republic, destroyed their ballistic missiles, in part, to better their chances of joining MTCR.” In October 1994, in order to make the enforcement of MTCR Guidelines more uniform, the member states established a “no undercut” policy, meaning if one member denies the sale of some technology to another country all members must adhere. The People's Republic of China is not a member of the MTCR but has agreed to abide by the original 1987 Guidelines and Annex, but not the subsequent revisions. China first verbally pledged that it would adhere to the MTCR in November 1991, included these assurances in a letter from its Foreign Minister in February 1992.

China reiterated its pledge in the October 1994 US-China joint statement. In their October 1997 joint statement, the United States and China stated that they agree "to build on the 1994 Joint Statement on Missile Nonproliferation." In 2004 China applied to join the MTCR, but members did not offer China membership because of concerns about China's export control standards. Israel and Slovakia have agreed to voluntarily follow MTCR export rules though not yet members; the regime has its limitations. Some of these countries, with varying degrees of foreign assistance, have deployed medium-range ballistic missiles that can travel more than 1,000 kilometers and are exploring missiles with much greater ranges and China in particular having deployed strategic nuclear SLCMs and ICBMs and satellite launch systems; some of these countries, which are not MTCR members, are becoming sellers rather than buyers on the global arms market. North Korea, for example, is viewed as the primary source of ballistic missile proliferation in the world today.

China has supplied ballistic missiles and technology to Pakistan. China supplied DF-3A IRBMs to Saudi Arabia in 1988 before it had informally agreed to follow MTCR guidelines. Due to its non-member MTCR status Israel is unable to export its Shavit space launch system to foreign customers though in 1994 the US Clinton administration did allow an import waiver for US companies to buy the Shavit. In 2002, the MTCR was supplemented by the International Code of Conduct against Ballistic Missile Proliferation known as the Hague Code of Conduct, which calls for restraint and care in the proliferation of ballistic missile systems capable of delivering weapons of mass destruction, has 119 members, thus working parallel to the MTCR with less specific restrictions but with a greater membership. India formally applied for membership to the group in June 2015, with active support from France and the United States, became a member on 27 June 2016 with the consensus of the 34 member nations. Over 20 countries have ballistic missile systems.

The MTCR has 35 members. Missile Technology Control Regime website Sarah Chankin-Gould & Ivan Oelrich, "Double-edged shield," Bulletin of the Atomic Scientists, May/June 2005