Kevin's Watch

But before they could reach safety, Drool appeared out of the cleft above them. The Cavewight was crawling, too crippled to stand. But in his fist he clutched a green stone which radiated intense wrong through the blackness of the clouds. His scream carried over the roar of the Lions:
'Crush! Crush!'

Set into the floor directly before it was the Illearth Stone.
The Stone was not so large as Foamfollower had expected it to be; it did not look so big or heavy that he could not have lifted in in his arms.

Murrin wrote:

Set into the floor directly before it was the Illearth Stone.
The Stone was not so large as Foamfollower had expected it to be; it did not look so big or heavy that he could not have lifted in in his arms.

No mention of its exact size, but LFB suggests it is no bigger than a Cavewight's over-sized hands, and there is no contradiction to that in TPTP - obviously FF is surprised that it is so small to have so much power.

Spoiler

In the heart of the whirling gale, the pillar of force, he knelt beside the Stone and put his arem around it like a man embracing immolation. New blood from his poisoned lip ran down his chin, dripped into the green and was vaporized.

With each moment, the conjunction of the two powers produced more and more might. Like a lifeless and indomitable heart of fury, the Illearth Stone pulsed in Covenant's arms, laboring in mindless, automatic reflex to destroy him rather than be destroyed.

With Callindrill, Troy, Quaan, Amorine, twoscore Bloodguard, all the Ranyhyn, and more than four thousand warriors, Lord Mhoram passed fore a time out of the world of humankind.

Slowly, the music transformed his conscious alertness, drew him into a kind of trance. He felt that he was still aware of everything, in the altered dimness of the Deep, but he felt no passage of time. In openings between the trees, he could see the Westron Mountains. By the changing positions of the peaks, he could gauge his speed. He appeared to be moving faster than a galloping Ranyhyn. But he felt no exertion or strain of travel. The breath of the song wafted him ahead, as if he and his companions were being inhaled by the Deep. It was a weird, dreamy passage, a soul journey, full of speed he could not experience and events he could not feel.

Night came--the moon was completely dark--but he did not lose sight of his way. Some hint of light in the grass and leaves and song made his path clear to him, and he went on confidently, untouched by any need for rest. The Forestal's song released him from mortality, wrapped him in careless peace.

Sometime during the darkness, he heard the change of the song. The alteration had no effect on him, but he understood its meaning. Though the Forest swallowed every other sound, so that no howls or screams or cries reached his ears, he knew that Fleshharrower's army was being destroyed. The song described ages of waiting hate, of grief over vast tracts of kindred lost, ages of slow rage which climbed through the sap of the woods until every limb and leaf shared it, lived it, ached to act. And through that melodic narration came whispers of death as roots and boughs and trunks moved together to crush and rend.

Against the immense Deep, even Fleshharrower's army was small and defenseless-a poaltry insult hurled against an ocean. The trees brushed aside the power of the ur-viles and the strength of the Cavewights and the mad, cornered, desperate fear of all the other creatures. Led by Caerroil Wildwood's song, they simply throttled the invaders. Flames were stamped out, blade wielders were slain, lore and force were overwhelmed. Then the trees drank the blood and ate the bodies--eradicated every trace of the enemy in an apotheosis of ancient and exquisite fury.

When the song resumed its former placid wafting, it seemed to breathe grim satisfaction and victory.

Soon after that--Mhoram thought it was soon--a rumble like thunder passed over the woods. At first, he thought that he was hearing Fleshharrower's death struggle. But then he saw that the sound had an entirely different source. Far ahead and to the west, some terrible violence occurred in the mountains. Red fires spouted from one part of the range. After every eruption, a concussion rolled over the Deep, and a coruscating exhaust paled the night sky. But Mhoram was immune to it. He watched it with interest, but the song wrapped him in its enchantments and preserved him from all care.

And he felt no concern when he realized that the Warward was no longer behind him. Except for Lord Callindrill, Troy, Amorine, Hiltmark Quaan, and two Bloodguard, Terrel and Morril, he was alone. But he was not anxious; the song assuaged him with peace and trust. It led him onward and still onward through a measureless night into the dawn of a new day.

With the return of light, he found that he was moving through a woodland profuse with purple and white orchids. Their soft, pure colors fell in with the music as if they were the notes Caerroil Wildwood sang. They enfolded Mhoram closely in the consolation of the melody. With a wide, unconscious smile, he let himself go as if the current which carried him were an anodyne for all his hurts.

His strange speed was more apparent now. Already through gaps in the overhanging foliage, he could see the paired spires of Melenkurion Skyweir, the tallest peaks in the Westron Mountains. He could see the high, sheer plateau of Rivenrock as the struggle it concealed continued. Eruptions and muffled booms came echoing from the depths of the mountain, and red bursts of force struck the sky at irregular intervals. But still he was untouched. His speed, his exhilarating, easy swiftness, filled his heart with gay glee. He had covered thirty or forty leagues since entering the Deep. He felt ready to walk that way forever.

But the day passed with the same timeless evanescence that had borne him through the night. Soon the sun was close to setting, yet he had no sense of duration, no weary or hungry physical impression that he had traveled all day.