Why would you tend to find lots of fossils in sedimentary rocks? why not in other rocks?

Sedimentary rocks form from layers of earth pressuring rock over time this rock become sedimentary. Since this rock is so old it is more likely to contain fossils than other rock formations. The other rock formations are usually newer and formed by lava or magma.

Maybe a horizontal because its a pattern

No, because you are more likely to see volcanic mountains where magma is rising along the mid-ocean ridge spreading to the center.