[brute]

Originally Posted by jchen

The following sentence contains either a single error or no error at all. If the sentence contains an error, select the one underlined part that must be changed to make the sentence correct. If the sentence contains no error, select choice E.

The Bear Gulch Limestone Formation a. in Montana is a sequence of bedded limestone layers b. up to 90 feet thick c. and approximately 8 miles d. across.
e. No error

Hint: Pay attention to prepositions.

I think it's (d)..... I haven't submitted my answer yet and I don't know if (d) is right. And I think it's (d) because it should be "wide", right? It is a preposition....

Thanks for any help given!

The whole sentence sounds all right to me.