卵化石（Egg Fossils）是什么？
主要为鱼卵化石（图9.70），由于鱼卵没有坚硬的外壳，形成化石所需的沉积条件非常苛刻，故鱼卵化石极为罕见，若连同产卵的鱼体化石同时出现在岩石底板上，则可谓观赏石收藏之珍品。哈萨克斯坦卡拉套化石保护区的晚侏罗世湖泊沉积物（叶状白云岩）内保存了一种类似鳕鱼的鱼化石，在其腹部还有大量的鱼卵化石。表明这条鱼正值产卵之际便遭受突如其来的掩埋。
化石形成（Formation of Fossil）是什么？
The forming of fossils requires several conditions.The first condition is possession of durable internal hard parts or shells which was relatively rapid buried in a sedimentary environment.The hard part of the ancient lives were comparatively easily preserved if the remains were buried quickly.But a few kinds were unchanged remainsfossils,such as mammuthus in tundra and insects in amber;the second condition is the presence of favorable habitats for organisms;the third condition is the time of diagenetic process.The remains can be replaced or permineralized within sediments if they are surrounded by high concentration of fluids carrying calcium carbonate,silicon dioxide,and mineral iron in solution.Thefossil might be preserved as imprints of animals tissues on the surface of the bedding planes of matrix,or as casts or mold,whichformed by infiling of secondary material in the holes left by dissolving of the hard parts of animals.
