in Thoreau’s Journal:

On Conantum Cliffs whose seams dip to the NW at an angle of 50º (?) and run NE and SW I find today for the first time the early saxifrage saxifrage vernalis in blossom—growing high and dry in the narrow seams where there is no soil for it but a little green moss.—following thus early after the bare rock—it is one of the first flowers not only in the spring of the year but in the spring of the world.—

It can take advantage of a perpendicular cliff where the snow cannot lie & fronting the S….This is the place to look for early blossoms of the saxifrage—columbine—& plantain leaved everlasting—the 1st 2 especially—

The crevices of the rock (cliff) make natural hot houses for them—affording dryness warmth & shelter.  It is astonishing how soon & unexpectedly flowers appear.