Pausanias Description of Greece 1.44.6

[6]
  On the road from Megara to Corinth are graves, including that of the Samian flute-player Telephanes, ¹ said to have been made by Cleopatra, daughter of Philip, son of Amyntas. There is also the tomb of Car, son of Phoroneus, which was originally a mound of earth, but afterwards, at the command of the oracle, it was adorned with mussel stone. The Megarians are the only Greeks to possess this stone, and in the city also they have made many things out of it. It is very white, and softer than other stone; in it throughout are sea mussels. Such is the nature of the stone. The road called Scironian to this day and named after Sciron, was made by him when he was war minister of the Megarians, and originally they say was constructed for the use of active men. But the emperor Hadrian broadened it, and made it suitable even for chariots to pass each other in opposite directions.

[6] As one proceeds from Megara to Corinth, there are tombs [ taphoi], including that of the aulos-player Telephanes of Samos. 150

The tomb [ taphos] is said to have been made [ poieîn] by Kleopatra, daughter of Philip son of Amyntas. There is also the tomb [ mnēma] of Kar, son of Phoroneus, which was originally a piled-up-mound [ khōma] of earth, but afterwards, in accordance with what the god [ theos] said-in-an-oracular-pronouncement [ khrēsai], it was adorned [ kosmeîn] with a kind of stone known as konkhītēs [‘in-which-seashells [ konkhoi]-are-embedded’]. The people of Megara are the only Greeks [ Hellēnes] to possess this kind of konkhītēs stone, and in the city also they have made [ poieîn] many things out of it. It is very white, and softer than other stone; embedded in it through and through are seashells [ konkhoi]. Such, then, is the stone itself. [As for rock formations that are also white…] There is a road called Skīrōnis—that is what it is called even to this day—and it is named after Skīrōn [= ‘he of the White Rock’]. This Skīrōn, when he was the military leader of the people of Megara, was the first, they say, to make [ poieîn] it [= Skīrōnis] a road usable enough for men who outfit themselves for travel. But then ‘King’ [ basileus] Hadrian broadened it, and made it more usable—so much so that even chariots [ harmata] could pass each other going in opposite directions.