1.  LDS.  Family Search: Internet Genealogy Service: Pedigree Resource File (index to CDs, online at FamilySearch.org):

CD#68 Husband: James A. CLARK; Birth: 1801, Washington, Virginia Marriage-1: 9 Jul 1829, Washington, Virginia Spouse-1: Mary M. NEWHOUSE; Birth: 1809, Washington, Virginia Marriage-2: 25 Aug 1853, Washington, Virginia Spouse-2: Mary E. CLARK; Birth: 1833, Washington, Virginia Marriage-3: Sep 1851, Washington, Virginia Spouse-3: Rebecca J. LOGAN; Birth: 1831, Washington, Virginia Source: Patty B. WHITE

CD#68 Robert W. CLARK; Birth: 1846, Washington, Virginia; Death: 8 Apr 1857, Washington, Virginia Charles Alfred CLARK; Birth: 16 May 1854, Washington, Virginia Father: James A. CLARK; Mother: Mary M. NEWHOUSE Source: Patty B. WHITE

This may be the worst example I've ever seen of incorrectly lumping people together just because they have the same name.  These are three different James CLARKs.  There is no Robert in the 1850 census with James & Mary (NEWHOUSE) CLARK, and Robert is too old to be the son of our subject or the other James CLARK.

2.  1860 Census Every-Name-Index/Images (online at Ancestry.com, Image #101 of 361):  Glade Spring P.O., Western District, Washington Co., VA, Roll M653_1383, p. 463, PN 99, 413/690, enumerated 11 Jul 1860, official enumeration date 1 Jun 1860 (extracted by Diana Gale Matthiesen):

James A Clark	34	M		Farmer		1400	Va
Mary      "	30	F		Housekeeper			Va
Charles   "	6	M					Va
William   "	1	M					Va

3.  Messages posted to the Clark Family Genealogy Forum (online at GenForum.com).