The megalithic monuments of Carnac and Locmariaquer; their purpose and age (1908)
http://www.archive.org/stream/megalithicmonume00lero#page/n1/mode/2up

Excavations at Carnac (Brittany): A Record of Archaeological Researches(1881)
http://www.archive.org/stream/excavationsatcar00milniala#page/n7/mode/2up Volume 1
http://www.archive.org/stream/excavationsatcar00milnuoft#page/n7/mode/2up Volume 2

Having a netbook and the links to online books is useful, I've found. (Especially for that one annoying person on a tour that knows more than me about something).

Composed at Carnac by Mathew Arnold

Far on its rocky knoll descried
Saint Michael's chapel cuts the sky.
I climted ; — beneath me, bright and wide,
Lay the tone coast of Brittany.

Bright in the sunset, weird and still,
It lay beside the Atlantic wave.
Ah though the wizard Merlin's will
Yet charm'd it from his forest-grave.

Behind me on their grassy sweep.
Bearded with lichen, scrawl'd and grey.
The giant stones of Carnac sleep.
In the mild evening of the May.

No priestly stem procession now
Moves (trough their rows of pillars old ;
No victims bleed, no Druids bow —
Sheep make the daisied aisles their fold.

From bush to bush the cuckoo flies,
The orchis red gleams everywhere ;
Gold furze with broom in blossom vies,
The blue-bells perfume all the air.

And o'er the glistening, lonely land,
Rise up, ll round, the Christian spires ;
The church of Carnac, by the strand,
Catches the westering sun's last fires.

And there, across the watery way.
See, low above the tide at flood.
The sickle-sweep of Quiberon Bay,
'Whose beach once ran with loyal blood 1

And beyond that, the Atlantic wide! —
All round, no soul, no boat, no hail ;
But, on the horizon's verge descried,
Hangs, touch'd with light, one snowy sail !

Ah ! where is he, who should have come
Where that far sail is passing now,
East the Loire's mouth, and by the foam
Of Finistfere's unquiet brow,

Home, round into the English wave?
— He tarries where the Rock of Spain
Mediterraneau waters lave ;
He enters not the Atlantic main.

Oh, could he once have reach'd this air
Freshen'd by plunging tides, by showers
Have felt this breath he loved, of fair
Cool northern fields, and grass, and flowers

He long'd for it — press'd on. — In vain !
At the Straits failed that spirit brave.
The sonth was parent of his pain.
The south is mistress of his grave.