I had thought that Big Clarke's special survey was obtained in 1841 when the British Government briefly allowed the purchase of 8 square mile blocks before protest from the authorities in Victoria resulted in the provision being overturned. However Isaac Batey, writing as Ramrod in the 1890's about the pioneers near Sunbury in 1846, stated that Big Clarke took up his survey in 1850. Isaac was right. This comes from Big Clarke's biography written by Hugh Anderson. (Australian Dictionary of Biography.)

In 1850, under the special survey clause of the Waste Lands Act, he successfully claimed 31,375 acres (12,697 ha) at 20s. an acre, and located it near Sunbury, twenty-five miles (40 km) from Melbourne. He next obtained the adjoining 31,000 acres (12,545 ha) under the Order-in-Council of 1847, both acquisitions displacing several pastoral licensees, and making a single property that stretched from Sunbury to the Sydney Road.

INCREDIBLE DETAIL.
There have been countless biographies and obituaries written about Big Clarke but this one takes the cake. He was actually born during a visit by his parents to London. When he started in business, his main aim was to develop what today would be called a credit rating; he always paid on time. When the depression struck the Port Phillip District in 1842 he was not ruined like many squatters,who were mortgaged to the hilt, were. My suspicion that Dowling Forest, whose extent and home station are specified, was named after his wife's maiden name is confirmed. The only mistake in the article is a typo; the name of his brother-in-law is given as James Hean instead of James Hearn.

MR. W. J. T. CLARKE.
Portland Guardian and Normanby General Advertiser (Vic. : 1842 - 1843; 1854 - 1876) Monday 12 February 1872 p 4 Article
or copy http://trove.nla.gov.au/newspaper/article/65426843into your search bar.

WHAT DID THE PRESS THINK ABOUT THE SPECIAL SURVEY?
THE GREAT LAND PURCHASE AT PORT PHILLIP.
The Melbourne Daily News (Vic. : 1848 - 1851) Monday 30 September 1850 p 4 Article
or copyhttp://trove.nla.gov.au/newspaper/article/226518414 into your search bar.