もっと良い組み方があるかもしれません。
ご参考までに＾＾；。

//堀________________________________________

field hori
{
	color = 16, 64, 64
	id = hori
	attr = mersh
	smooth = off
	alt = -96
}

field stone11 : hori
{
}

field stone12 : hori
{
}

//その他________________________________________

field stone
{
	color = 64, 128, 64
	attr = rock
}

field stone7 : stone
{
}

field stone8 : stone
{
}

field stone9 : stone
{
}

field stone10 : stone
{
}