Simplify the following text for a Grade 8 native English-speaking person.
Original: Slate quarrying began in the hills above Tywyn in the 1830s , but although many small quarries and test levels were established , only one major quarry was developed in the region , at Bryn Eglwys , 7 m north east of the town .
Simplified: Slate quarrying began in the hills above Tywyn in the 1830s . Although many small quarries and test levels were established , only one major quarry was developed in the region .