If the time shall ever come when, through the labor of the geologist, all that can possibly be learned in regard to the structure and development of the earth shall have been learned, the occupation of the geologist would be gone.

1. 划线部分是 if 从句中修饰 the time 的定语从句，因太长而被后移，也叫被谓语分隔。

2. 在这个定语从句中，又包含着一个定语从句：that can possibly be learned in regard to the structure and development of the earth，修饰 all。

3. 去掉这个定语从句后， all shall have been learned。现在已经很清楚了: all 是主语，shall have been learned 是谓语。

4. in regard to the structure and development of the earth，这是介词短语，意为：所有关于地球结构和发展的知识。in regard to 看作一个固定的“短语介词”，意为“关于”。不错，后面接的就是名词词组the structure and development of the earth。

【翻译】通过地质学家的努力，所有关于地球结构和发展的知识都将被学会，如果这一天（这个时间）到来的话，那么地质学家的职业就会消失。