Coinage of the Chinese dynasty
The Southern Song dynasty refers to an era of the Song dynasty after Kaifeng was captured by the Jurchen-led Jin dynasty in 1127. The government of the Song was forced to establish a new capital city at Lin'an (present day Hangzhou) which wasn't near any sources of copper so the quality of the cash coins produced under the Southern Song significantly deteriorated compared to the cast copper-alloy cash coins of the Northern Song dynasty. The Southern Song government preferred to invest in their defenses (as its incapable military easily fell to the Jin dynasty) while trying to remain passive towards the Jin dynasty establishing a long peace until the Mongols eventually annexed the Jin before marching down to the Song establishing the Yuan dynasty.
Coins from the Song dynasty have appeared in variants written in either standard (top-bottom-right-left) or clockwise (top-right-bottom-left).
The Southern Song dynasty saw the emergence of paper money, while coins were increasingly becoming a rarity. Iron cash coins also started to be used in greater numbers, at first due to the lack of copper, but later even as more copper was found the production of iron cash coins remained cheaper and an abundance of iron made it more attractive for the government to produce, while several problems such as the fact that iron is harder to inscribe, and that iron corrodes faster ensured the continued production of copper cash coins. Despite the chronic shortages of copper the Southern Song used special coins as a form of psychological warfare against Jin army defectors, and copper coins (and later silver sycees) would remain the standard of administration even for the newly introduced paper money.
Background.
The Northern Song dynasty saw the reunification of most parts of China proper and also of its currency. The Northern Song dynasty saw the widespread usage of "matched cash coins" which used different types of Chinese calligraphy for the same inscriptions and the reintroduction of cash coins of different denominations. Government corruption would lead to the Northern Song government producing large quantities of iron cash coins by the end of the reign of Emperor Zhezong.
By the time of the Chongning Zhongbao (崇寧重寶) cash coins of the Emperor Huizong, 10 "wén" cash coins had become the norm as the government used it as a method to confiscate the wealth of the people to enrich its treasury. In a story dating to the Northern Song dynasty time period, a man purchasing a bowl of soup is used to illustrate the hardship caused by the lack of 1 "wén" cash coins, which are known as "Xiaoping" cash coins (小平錢). 
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The story relates that a patron bought a bowl of soup and paid for it with a "10 cash" coin. The soup seller did not have any small change and so encouraged the customer to eat more and more soup. The customer continued to eat but finally sighed and said, "it is fortunate that my coin is only a "10 cash". If it had been a "100 cash" it would have killed me!"
 - Translated by Gary Ashkenazy of the "Primaltrek" website from Mandarin Chinese. 
These 10 "wén" cash coins were so overvalued by the government that they were eventually devalued by the market until they were only worth the equivalent of 3 cash coins.
History.
The Southern Song would suffer from what had been called "currency famines" or Qian Huang (錢荒), during the mid-13th century, this was because the production of bronze coinage had fallen to merely 2 to 3% of what it had been under the Northern Song, meanwhile the relative value of silver compared to bronze had steadily increased leading to the Song government adopting silver as the new standard as the value of silver would remain pretty much standard at the entire duration of the Southern Song while the value of bronze would fluctuate enormously.
The Song dynasty had several "monetary regions" which all had their own separate combination of bronze, and/or iron coins, paper money, and silver sycees in circulation. These separate regional currency standards created distinct regional characters that would often hinder interregional trade between them. The Song government's general inability to create enough bronze wén coins to circulate helped strengthen this monetary diversity that would impede trade, even though the Northern Song had enough bronze for this demand and to even create large coins called "biscuit coins", the southern regions lacked these resources after they had lost the North to the Jin.
Despite the large variety in different media of exchange, Southern Song dynasty documents always measure prices in bronze coins ("guàn" 貫, and "wén" 文), which includes the value of silver bullion itself. After Wang Anshi reformed the fiscal administration of the Southern Song between 1069 and 1085, silver became a vital element in administrative book-keeping, especially in certain regions rich in silver such as modern-day Sichuan.
In the year 1173 during the reign of Emperor Xiaozong the period title was proclaimed to be Chunxi with the "Chun" written as "纯". Only six days later after this proclamation, the "Chun" was officially changed to be written in Hanzi as "淳". The Tongan mint in the Anhui region produced a very small quantity of Chunxi Yuanbao (纯熙元寶) iron cash coins with the chun written as "纯".  These diminutive iron coins today are considered to be very rare. Furthermore, during the beginning of the Chunxi period, bronze cash coins produced from this era and continuing to the very end of the Southern Song dynasty, tended to have their inscriptions (or legends) written in a form of Chinese calligraphy that is today known as the "Song style script" or "regular script". For this reason, there are in fact fewer number of varieties of bronze Song dynasty cash coins from this period onwards compared to those from earlier periods.
Until 1179 the Northern Song era's policies of casting coins in varying typefaces continued but after this year most coins tended to only have Regular script inscriptions. Beginning in 1180 coins cast by the Southern Song government started to cast the reign year on the reverses of coins as well as mint marks in order to stop forgeries from circulated, this was because the technology to cast inscriptions on both sides of the coins hasn't been adopted yet by private mints at the time. From 1180 until the end of the Song dynasty very few bronze coins were produced by the government as the preference went to iron, this was because bronze cash coins needed to have a specific typeface which was more intricate to produce.
A constant problem for the Song government was the outflow of its currency, particularly to the Jin dynasty which didn't produce much coinage of its own. This outflow of coins eventually caused the Song government to produce more paper money in order to sustain its economy.
By 1160 bronze coins had become a rarity, and became largely an abstract measurement of value rather than a tangible currency, the most important attribute of bronze coins after this year was as a measurement for the value of other currencies, by 1161 a shortage in wén coins had forced the Southern Song government to halve the salary of their soldiers and rather than pay them 50% in Huizi, 30% in silver, and only 20% in bronze coins. After 1170 the Song court established Huizi paper money on a permanent basis based on the "Pinda" (品搭) formula that mandated that taxes were only half paid in coin and the other half in Huizi notes. This formula would prove successful as it increased the value of Huizi in circulation, while also increasing the demand for the uncommon wén coins. Huizi notes were increasingly used for commercial purposes while bronze coins were often being hoarded up as savings, although the Huizi notes were also hoarded up as savings, the government had set up a 3 year expiry term so people would have to constantly renew their banknotes at government offices to stop them from hoarding the value up like what happened with bronze coinage.
Due to the constant threat of the Mongol Empire and increased military expenditures the Song government started to cast more coins leading to inflation. Eventually coins became a rarely used item in Lin'an causing the Southern Song government to start producing small coin tallies called Qian Pai (錢牌) in denominations of 10, 40, 100, 200, 300, and 500 wén, in reality however the denominations were discounted per 100 wén (often at 30%) and were worth less on the actual market, an example of this would be 77 wén for official business, 75 wén for trading purposes, and could be discounted to as low as 56 for writings. The majority of Qian Pai tablets tend to have the description "(for) use in Lin'An Prefecture" (臨安府行用), the contemporary capital city. The Qian Pai are attributed to the Jingding period (1260–1264).
As the Mongols started to advance Southwards the last 3 emperors of the Song dynasty did not cast any coins as they had neither the time to set up any mints nor the resources to produce any cast coins.
List of cash coins produced by the Song dynasty.
The coins produced during the Song dynasty period include:
Mintage figures and money supply.
Bronze cash coins.
Bronze cash coins were produced is large amounts in the prior era of the Song, this can be partially explained due to population growth as the population grew from at least 32.000.000 people in 961 to at most 120.000.000 in 1193. For example, during the reign of Emperor Taizong 800.000 strings (or 800.000.000 cash coins) were cast, while during the reign of Emperor Yingzong the annual production rose to 3.000.000 strings. 
By the time of the Jingkang incident the government of the Song dynasty had accumulated 98.000.000 strings, and that 30.000.000 strings circulated among people. This indicated that while a large number of cash coins were being produced during the Northern Song dynasty period, only some of them reached general circulation among the people. Even if the number of cash coins in strings was only around 800 per string, the total number of Song dynasty cash coins that was produced by the end of Song dynasty period would be around 90.000.000.000. However, an even larger number of cash coins was likely cast due to the fact that the currency of the Song dynasty had become the universal currency of the Far East at the time and a large number of cash coins was exported. 
Meanwhile, the annual output of cash coins had greatly declined during the Southern Song dynasty period reaching only an average of 200.000 strings per year and often far less, this was due to a combination of both high minting costs and high mining costs. The copper shortage was so bad that it became a frequent event for the emperor to issue edicts demanding that private citizens would deliver all their copper-alloy utensils and other possessions to the mints. The copper shortage also meant that, compared to the cash coins of the Northern Song dynasty period, the Southern Song coinage contained 25% less copper.
The success of Northern Song dynasty cash coins domestically and internationally made it difficult, even at peak production, to produce a sufficient number of coins for the market, and to restore the elasticity of the money supply the government issued paper money to secure the payment of taxes.
Iron cash coins.
Iron cash coins played an important role during the Song dynasty period and approximately 900.000.000 iron cash coins were produced annually. In 1080 there were 26 mints, 9 of them produced iron cash coins. 
Most iron cash coins circulated in the south alongside bronze cash coins, but during the Southern Song dynasty period their circulation was supplemented with paper money alleviating the issues caused by the regional copper shortage. Meaning that while iron cash coins still circulated there during the Southern Song period, they were no longer as important as they were during the Northern Song period.
Cash coins issued for Jin Army defectors.
In the year Shaoxing 1 (1131) the military forces of the Song and Jurchen Jin dynasties were encamped opposite to each other on each side of the Yangtze River, General Liu Guangshi (劉光世) created a special cash coin-like "trust token" with the inscription Zhaona Xinbao (招納信寶) which could be translated as "Treasure (coin) that recruits (Jin dynasty) soldiers who desire to return to their home" and