Here's more from the link cited by Aelius concerning the loss of the Cotton MSS:

In the absence of any meaningful statistics, the best way of conveying the catastrophic nature of the losses in the Ashburnham House fire is by a random roll call of some of the victims.(13) Cotton's pride and joy, the fifth-century Greek Genesis (Otho B. VI), one of the earliest illustrated Christian manuscripts in existence, was reduced to a pile of cinder-like fragments.(14) Cotton possessed two of the four surviving letters patent of King John recording the grant of Magna Carta. One of these, now Cotton Charter XIII. 31a, was the only one with the Great Seal still attached. In the heat, not only was the text damaged but the seal was left as a shapeless blob.(15) The bull confirming the title 'Defender of the Faith' on Henry VIII (now Vitellius B. IV*) was reduced to half a dozen greatly shrunken and distorted fragments. Otho A. XII contained unique exemplars of two key texts for the Anglo-Saxon period, Asser's Life of Alfred and The Battle of Maldon, together with other Old English material.(16) Although 40 folios of the original 155 were eventually recovered, both Asser and Maldon perished completely. Among the chronicle texts which were lost or very badly damaged were the earliest manuscript of Gildas (Vitellius A. VI),(17) the 'G' manuscript of the Anglo-Saxon Chronicle in Otho B. XI,(18) and the only extant manuscript of Æthelweard's chronicle (Otho A. X).(19) Cartularies from such houses as Lenton (Otho B. XIV),(20) St Albans (Otho D. III) and St Augustine, Canterbury (Otho B. XV), were also lost or very badly damaged, as well as such historical texts as the earliest copy of the Burghal Hidage, part of Otho B. XI.(21) Among the illuminated manuscripts ruined in the fire might be singled out a portion of an early eighth-century gospel book from Northumbria, Otho C. V, if only because another fragment of this manuscript survives intact in Cambridge, Corpus Christi College, MS 197B, and shows that it was an insular gospel-book from the greatest period of Northumbrian illumination.(22) These are mostly medieval examples. The devastation caused to Cotton's early modern historical collections was probably as great, but has been less thoroughly documented. It is a measure of the richness of Cotton's library that, despite such losses, it still remains an incomparable source for the history, literature and art of medieval and Tudor England.