Something a little cleaner to read

local Sizelength = 2
local sizeFront = 2

function verwood()
  local height = 0
  local detectx = turtle.detect

  local goUp = function()
    turtle.digUp()
    turtle.up()
    height = height + 1
  end

  local goDown = function()
    turtle.digDown()
    turtle.down()
    height = height - 1
  end

  local turnAround = function()
    turtle.turnRight()
    turtle.turnRight()
  end

  function chop4left()
      while goUp() do
        turtle.dig()
      end

      turtle.turnRight()
      turtle.forward()
      turtle.turnLeft()
      goDown()

      while height>0 do
        turtle.dig()
        goDown()
        turtle.digDown()
      end

      turtle.turnRight()
      turtle.back()
      turtle.back()
  end

  if detectx() then
    turtle.dig()
    turtle.forward()
  end
  if not detectx() then
    turtle.back()
    goUp()

    while detectx() do
      turtle.dig()
      goUp()
    end

    for i = 1, height do
      goDown()
    end
  else
    turtle.forward()
    turtle.turnLeft()

    if detectx() then
      chop4left()
    else
      turnAround()
      while detectx() do
        turtle.dig()
        goUp()
      end
      turtle.turnLeft()
      turtle.forward()
      turtle.turnRight()
      while height > 0 do
        turtle.dig()
        goDown()
      end
      turtle.turnLeft()
      turtle.back()
      turtle.back()
    end
  end
end

function walkver()
  if turtle.detect() then
    verwood()
  end
end

local stepsback = Sizelength * 2 + 1

function minefront()
  for i = 0, sizeFront do
    turtle.forward()
    walkver()
  end
end

for i = 0, Sizelength do
  minefront()
  turtle.turnLeft()
  walkver()
  turtle.forward()
  turtle.turnLeft()
  minefront()
  turtle.turnRight()
  walkver()
  turtle.forward()
  turtle.turnRight()
  walkver()
end

turtle.turnRight()

for i = 0, stepsback do
  turtle.forward()
end

turtle.turnLeft()