Step 1: What tectonites are.
Tectonites are rocks whose inside fabric, such as foliation and lineation, was shaped by the stress they faced during earth movements. Their fabric acts like a record of that stress.
Step 2: Check Statement I.
Statement I says these fabrics show the direction and size of past stresses and let us rebuild past tectonic events. Since the fabric records the strain, reading it back gives the stress history. So Statement I is correct.
Step 3: Check Statement II.
Statement II says tectonites give insight into mountain building and continental collision. Those are exactly the large scale events that deform rocks and leave such fabrics, so studying tectonites does reveal them. Statement II is correct.
Step 4: Both stand together.
Statement II is really an application of the idea in Statement I, so the two support each other and both hold true.
Step 5: Pick the option.
Since both statements are correct, the right choice is the one saying both are correct.
Step 6: Answer.
Both Statement I and Statement II are correct.
\[ \boxed{\text{Both Statement-I and Statement-II are correct}} \]