The group listed here that contains silica in its surface covering is the:
ciliates
red algae
diatoms
water molds

The group that contains silica the diatoms.  Diatoms are unicellular algae. They have a silica based cell wall known as a frustule, which gives each diatom a particular shape.

Diatoms exist as single cells  though some maybe found in colonies that create beautiful shapes which can be leaf - shaped, oval, round and other shapes.

The outer shells of diatoms are used in industry in the manufacture of many products such as toothpaste. The gritty texture in toothpaste is due to addition of diatoms .

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".

events in order:

1.       vishnu schist

2. zoroaster granite

3. bass limestone

4. hakatar   shale

5. igneous intrusion

6. shinumo quartzite

7. dox sandstone

8. tapeats limestone

9. bright angel shale

10. muav limestone

11. temple butte limestone

12. redwall limestone  

nonconformity

answer: the unkar group shows angular unconformity because the layers are turned at angle.

unconformity

answer: specifically the angular unconformity occurs between the cambrian and precambrian rocks. the dox sandstone, shinumo quartzite, hakatar shale, and bass limestone have been filled. an angular unconformity occurs between the cambrian and precambrian rocks. the dox sandstone, shinumo quartzite, hakatar shale, and bass limestone have been filled.

disconformity

answer: the disconformities aremarked irregular lines between the sedimentaryrocks layers.