请教老师们：

Squeezing through a cleft in the rocks, the pot-holers arrived at an enormous cavern, the size of a huge concert hall.

After switching on powerful arc lights, they saw great stalagmites - some of them over forty feet high - rising up like tree-trunks to meet the stalactites suspended from the roof.

1）the size of a huge concert hall 现代语法叫作无动词分句吗？传统语法叫什么呢？ some of them over forty feet high, 也可以说成：“，some of which were over forty feet high " 吗？

2）另外，-rising up...这里是see sb/sth doing sth - rising up 表示正在进行，似乎很难理解？这是定语，不是宾补？

Round about, piles of limestone glistened in all the colours of the rainbow. In the eerie silence of the cavern, the only sound that could be heard was made by water which dripped continuously from the high dome above them.

3）词典例句：Dewdrops sparkle [glisten] in the morning sun.  露珠在晨光下闪闪发光。

piles of limestone glistened in all the colours of the rainbow：成堆的石灰石在彩虹的所有颜色下闪闪发光？这是什么意思呢？很难理解？