The flow of gas was so heavy that it clogged his drills with maltha and sand, and from then to now the gas has been escaping.
"The New North"
Agnes Deans Cameron
Among different bituminous substances, the names naphtha and petrolium have been given to those which are fluid, maltha, to that which has the consistence of pitch, and asphaltum to that which is solid.
"The American Woman's Home"
Catherine E. Beecher and Harriet Beecher Stowe
The context leaves no doubt that he means Batn Nakhla, and that maltha is a mistake for Naltha.
"Personal Narrative of a Pilgrimage to Al-Madinah & Meccah"
Sir Richard Francis Burton