For, though the freshly fallen snow of these heights is, for the most part, at a lower temperature than that of 0 degree, the first hours of warm sunshine melt its surface and 
(the freshly fallen snow of these heights; is; ) (the first hours of warm sunshine; melt; its surface; L:at a lower temperature than that of 0 degree)
the freshly fallen snow of these heights the first hours of warm sunshine
is melt
its surface L:at a lower temperature than that of 0 degree