This post opens a series on Confederate artillery units in and adjacent to the West Woods. In the morning phase of the battle (5:30 to 8:30), artillery units were positioned, among other places, in the Philadelphia Brigade Park which was then an open field. In the second phase of West Woods action (8:30-10:30), units were positioned on Hauser's Ridge 600 yards west of the West Woods boundary while other units were literally in the woods south of the Dunkard Church.
Thanks to the Cope/Carman maps, we can determine the identities of most Confederate artillery batteries in and adjacent to the West Woods and can do so nearly hour-by-hour. There are, still, some mysteries. The first illustration is a detail from the Cope/Carman map showing unit locations from 9:00 to 9:30 a.m.. This section of the map depicts three artillery formations. McCarthy's Battery is clearly labeled; two others are unidentified; I have marked these two units A and B. Very few units were unidentified in the Cope/Carman map series--who were these artillery units? The blue arrow associated with McCarthy's Battery indicates the view angle of the third picture below. Note all illustrations can be enlarged by clicking on them.
Unit A (for want of any other description) is mentioned by Col. Alfred Sully of the First Minnesota in his Official Report on September 20. After describing the regiment's advance across the cornfield, he states that the regiment came "into a woods close to the enemy and in front of our line of battle. Here we were posted behind a rail fence. The enemy soon appeared in force on the left of the brigade, opened a very severe fire of musketry on us, while some of their artillery in front of us also opened on us." This artillery, according to the map, lay in front of the 13th Virginia. Who were they? [1a]
Unit B, which occupied a knoll just south of the Hauser farmstead, also remains a mystery. The second picture here shows the knoll in the far distance viewed from the Poffenberger farmstead.
The third unit recorded on the map is McCarthy’s Battery also known as the First Company, Richmond Howitzers. It was a small unit that may have played some part in slowing Gorman's Brigade's advance from the West Woods.
The Richmond Howitzers was founded in 1859 by George Wythe Randolph, a grandson of Thomas Jefferson, and a Richmond lawyer. By May 1860, the Howitzers had been organized into three companies. An observer wrote that all three, "were made up largely of young business men and clerks of the highest grade and best character from the city of Richmond, but included also a number of country boys, for the most part of excellent families, with a very considerable infusion of college-bred men." In April 1861, the second and third companies became part of the First Virginia Artillery Regiment. [1b]
The First Company participated in the Battle of Williamsburg on May 5, Seven Pines (May 31-June 1), the Seven Days’ Battles (June 25-July 1), and were at Second Manassas.  By September 1862, the company was known as McCarthy's Battery and was reported as being comprised of two 10-pounder Parrotts and two 6-pounders. Only two pieces, the 6-pounders, however, were brought into action on September 17 at Sharpsburg. 
Led by Robert Meriwether Anderson (1822-1880), the battery was part of McLaw's Division. It included thirty-two enlisted men and remained in line of battle all day, losing one killed and one wounded.
Ezra Carman writes: "Two guns of the 1st Company, Richmond Howitzers, under Lieutenant Robert M. Anderson moved on Semmes's right, but the open, exposed field was no place for artillery. It could not live under the fire that swept it, and--under orders--Anderson withdrew his guns to the high ground in rear, south of the Houser [sic] farm." 
The position of the battery during the fight swirling around the Alfred Poffenberger farmstead was about 300 yards due south of the farmstead. The third picture to the left shows the view northward from the battery's position.
According to Carman, there were two other companies of the Richmond Howitzers at Antietam. They are the Second Company, Watson's Battery, and the Third Company, Smith's Battery. A section of Watson's Battery supported Stuart at Williamsport on September 19 and withdrew the night of the 20th along with the rest of Stuart's force. Carman does not report activity for the Second Company. 
I would like to acknowledge the invaluable help provided by Capt. Wayne Rowe of the 1st Co. Richmond Howitzers (reenactment). Any errors in this post, however, are mine. The website of the group can be found at: http://1stcorichmondhowitzers.com.
[1a] This unit was probably Pelham's Battery. Carman, describing action between 7:30 and 9 a.m., writes: "Pelham's Battery, supported by the 13th Virginia and a small cavalry force, was left near the northwest corner of the West Woods." (p. 247). Describing the advance of the First Minnesota he writes: "The regiment now …pushed through the woods to a rail fence bordering them on the west, and halted at the fence, beyond which was a cornfield on gradually rising to the crest of Hauser's ridge (on which was a small piece of woods concealing the 13th Virginia in support of Pelham's Battery). …Immediately on the Minnesotans coming to a halt, the skirmishers of the 13th Virginia opened fire from the cornfield but were driven back to the woods about 220 yards distant, soon after which Pelham's battery opened fire." p. 261.
[1b] Encyclopedia Virginia (The Virginia Foundation); "Four Years Under Marse Robert," by Major Robert Stiles retrieved from http://www.howitzers.com/unit.htm.
 Encyclopedia Virginia (The Virginia Foundation).
 "Like almost all Civil War units, the First Richmond Virginia Howitzer Company was often known by an alternate designation derived from the name of its commanding officer. Names of this type used by or for the company are: John C. Shields' Artillery, William P. Palmer's Artillery, Edward S. McCarthy's Artillery, and Robert M. Anderson's Artillery." Typescript notes, Unit Vertical File, Visitor's Center Files, Antietam National Battlefield. Edward McCarthy did not go to Antietam and instead remained in Richmond overseeing the repair and maintenance of the two 10-pounder Parrots (Wayne Rowe correspondence, 2.6.2010).
 Some accounts state that the battery left their 2 6-pounders at Leesburg at the opening of the campaign. Wayne Rowe offers, however, that "There was only one section at Antietam and it was lead by Lt. Anderson and it contained the 6-pounders and not the 10-pounder Parrotts." (Wayne Rowe correspondence, 2.5.2010). See also, http://1stcorichmondhowitzers.com/RHcivilwarhistory
 Ezra Carman, The Maryland Campaign of September 1862, p. 258.
Anderson, like the founder Randolph, was from a long line of Virginia gentry and was a direct descendant of Meriwether Lewis of the Lewis and Clark Expedition (his grandmother, Jane Meriwether Lewis (1770-1845), was Meriwether Lewis’ sister); Genealogies of the Lewis and Kindred Families, John Meriwether McAllister and Tura Boulton Tandy, eds., (Columbia, MO.: E.W. Stephens Publishing Co., 1906), pp. 23, 47-49. Anderson survived the war and settled in Essex Virginia. He married Harriet Shore Lewis (1839-1892) in Essex on Christmas Eve, 1864. They produced five children. On November 9, 1880, his house caught fire and Anderson died from inhaling flames while rescuing his effects. After Robert’s death, the mother and the children relocated to Richmond. Lewises, Meriwethers, and Their Kin, (Richmond, Va., 1938; reprinted for Clearfield Company by Genealogical Publishing Co., Baltimore, MD, 2008), p. 117; Warner Broaddus’ Genealogy retrieved at http://members.cox.net/broaddus/pafg07.htm.)
 Carman, p. 263. Carman also notes that the 15th Massachusetts suffered additional "fire of several pieces of artillery that were run-up on Hauser's Ridge and poured an incessant stream of canister and shrapnel along the entire front of the three right regiments of Gorman's brigade and upon the exposed and defenseless lines in rear." [p. 263] Typically, canister was ineffective beyond 400 yards. The distance to Hauser's Ridge from where the 15th stood is over 600 yards. Could the canister have come from McCarthy's Battery?
 Carman, p. 376. The two batteries were part of the reserve artillery led by Brigadier General William Pendleton. The units formed under Col. John Thompson Brown's Battalion along with three other Virginia artillery outfits: the Powhatan, Salem, and Williamsburg Artillery. Carman, p. 433.