four
o’clock
Sulphur springs sometimes stopped their way , and they had to go round them . In some places the sulphur had formed crystals among other substances , such as whitish cinders made of an infinity of little feldspar crystals . In approaching the first plateau formed by the truncating of the lower cone , the difficulties of the ascent were very great . Towards four o'clock the extreme zone of the trees had been passed . There only remained here and there a few twisted , stunted pines , which must have had a hard life in resisting at this altitude the high winds from the open sea . Happily for the engineer and his companions the weather was beautiful , the atmosphere tranquil ; for a high breeze at an elevation of three thousand feet would have hindered their proceedings . The purity of the sky at the zenith was felt through the transparent air .