From the AKC website. Silky Terriers lineage is derived from Yorkies.
"Developed at the end of the 1800s in Australia, the Silky Terrier was created when a number of Yorkshire Terriers from England were brought into parts of Australia and bred to Australian Terrier bitches in an attempt to improve coat color in the blue and tan Australian Terrier. The resulting litters produced individuals shown as these three different breeds. The Silkys were then bred together until a recognized type was fixed."
Here is the link:
American Kennel Club - Silky Terrier